I've been working on my gear for years (far too long) and here's some insights into it... I'd say I don't have a lot of stuff in general, but more than most minimalist travellers, because I've not yet got to the point where I'm not completely indifferent to fashion and not wanting to wear the same black stuff everyday... but a lot better than when I started off.
I'm going indefinitely around the world with just a 29L backpack and can fit all the clothes following in addition to toiletries, electronics and quite a bit of other stuff. It allows for lots of mix and matching so I don't always have to look the same without carrying tons of stuff (but still more than I'd like at the moment). It's all quite expensive stuff too, which I bought thinking I'd need the best and on suggestions on how good the quality and functionality is... but then, it might have been better to buy cheaper stuff, because even though they don't "perform" as well, if they get damaged, it's a lot less of a worry than replacing a £70 pair of pants, right?
So, here's what I got:
1 black smartwool t shirt Standard black merino wool t shirt, looks like any other t shirt and goes with everything.
1 white Silic t shirt This thing I got from a Kickstarter campaign. I always wear white t shirts and didn't want to bring one travelling because they attract stains and I didn't want to have to do laundry all the time. This one kind of removes that worry as it's hydrophobic and repels all kinds of stains. Drop wine and soy sauce on this and it'll roll right off. Not all magical though, as it's quite see through (more so on darker people). I think the guy running the Kickstarter has kinda gone out of business so you won't be able to get one, but Threadsmiths do the same kind of thing, but in cotton. Pros of the Threadsmiths shirts are they're not as see through and cotton doesn't smell as bad as polyester can... but wrinkles more, and they advise against ironing so I'm not sure what to do on that one, as ironing out wrinkles and creases can destroy the hydrophobic properties of the shirt, which will reduce it to being just an ordinary - and very expensive - white t shirt.
1 pair of Rohan Jeans Plus and 1 pair of black Bluffworks pants Two pairs of pants! When I started buying stuff, I didn't want to give up jeans yet and like you, wanted variety and to switch between being smart and casual at times. The Bluffworks pants are supposed to be great all purpose ones and can be the only pair you'd need, but I'd miss jeans (a staple of my look) too much and didn't want to always be wearing smart looking trousers. So I got both. They're both similar in their properties such as being wrinkle resistant, quick drying, extra useful pockets and looking like NORMAL clothes. For job interviews, formal events or smartening up, I stick on the Bluffs and the Jeans Plus goes on for mostly everything else. Today though, I kind of don't want or feel the need for two pairs of pants. I'll stick with them for now as I'm going to appreciate being able to mix things up, but for the most part I don't overly care that much about what I wear and having one pair of pants would make life really simple. I'd probably just go for a pair of black Outlier Slim Dungarees now. They sound incredible and not having another pair of pants in my backpack would free up quite a bit of room.
1 Ministry of Supply Atmos White T Shirt I have ANOTHER white t shirt in there which seems kinda excessive as I have one that repels stains and all that already. But as I said before, it's not perfect, is kinda see through and I'm not sure how well it'll hold up, so I got this as a backup. Seems like any normal white t shirt and has lots of great properties, like being stain, odour and wrinkle resistant. Those are all prety important for me, especially the wrinkle resistance. When picking clothes I always go mad for stuff that resists wrinkles, as I hate the fuck out of creases and won't have access to an iron.
1 Grey All Saints Mode Merino Jumper Dunno if All Saints is international, but I love their stuff. Looks great and their Mode Merino stuff is lovely... but REALLY expensive. I pick up their merino wool stuff on Ebay most of the time as they're in decent condition and cheaper. I find they look nicer than some of the other wool long sleeve tops out there. Not too warm or cold, this.
1 Wool and Prince button down shirt SUPER expensive, but again, I want a shirt that resists wrinkles and odours and this one does it very well. I picked a blue oxford, but am returning it for their upcoming navy colour. Was tempted to go for their new black one, too. These are great because you can pick a solid coloured shirt to layer up. I can wear it with the black and white t shirts I have, opened or closed, or over the grey All Saints jumper, why not. Navy and black I think would be better as they go with everything, you can layer it up opened or closed, you can wear it with a suit for a formal look or with a hoody and go casual. And people won't notice you're wearing the same shirt as much as a patterened one or more in your face colour. I would prefer a stain resistant shirt, though... especially white. There are a few on Kickstarter that are stain repellant, but cotton.
1 black All Saints Mode Merino Hoody This was pretty expensive, but I can't exist without a hoody (yet). It's very lightweight and looks awesome, and because it's not too thick, if I want to smarten up a bit, I can tuck the hood behind my back so it looks like a cardigan. Goes great with all my other bits, packs away small, looks nice, is merino wool and adds a bit of warmth if you need it.
1 BauBax Travel Blazer There are a few travel blazers out there already, but they're all very expensive. The BauBax blazer was on Kickstarter and I got it at the early bird price. Like yourself, I wanted to be able to jump into looking smart if I wanted to, but couldn't bring any of my blazers from home as they're not worth the hassle of all the room they'd need and looking crap after coming out of a backpack and needing ironing. The BauBax blazer I got because it kind of removes all that by being wrinkle resistant. It's got all these other cool features, like gloves, pockets for loads of stuff, a hood and pillow which I don't overly care too much about as I just want a low maintenance blazer that looks good and isn't too expensive and that's what it is. I haven't got this yet as they're delivering over the next few months, but I'm excited for it and I know it'll fit in my bag as I've tested using a bigger and bulkier blazer to check! Again, this blazer is easy to mix with all the other things I own to change up my look, whether I want to look casual or formal for a job interview. There's a similar thing on Kickstarter now which I prefer as it's wrinkle resistant AND hydrophobic, reversible and stain repellant. It sounds perfect. Search for "the only blazer" on there.
1 Montbell Down Jacket This doesn't look amazing (one of my friends said I look like I'm wearing a black trash bag haha), but zero fucks are given. It packs down impossibly small so it takes up no room and keeps me warm. It's hard for me to care about what I look like when I feel like such a badass wearing something like this keeping me warm and toasty. And I don't have to find anywhere to put it as it packs so small. It hides away in my backpack for when I need it and basically vanishes when I don't. Layering it with all the other nice stuff I own, I don't even need to own a bigger jacket or anything. I can wear it under the BauBax blazer or my hoody and be perfectly warm and when I'm indoors, just stuff it away.
1 Marmot Mica rain shell Another versatile little thing that doesn't look fashionable, but works. Windbreaking, folds away into its own pocket and takes up no room, I can chuck it on anything else I'm wearing and not have to worry about the rain... with a good down jacket and rainshell paired up, you won't have much room taken up and you'll be ready for any weather. Looking back, I'd probably want a decent stormproof umbrella, but it doesn't hurt having this.