Here's something I posted a while back.
HOW TO SPEND YOUR GOLD
"Oh no," you might say, "my character has amassed large quantities of generic medieval currency, and despite the fact that I have spent several hours playing as that character, I have no idea on what my character would spend such vast wealth. And though I have trawled the Player's Handbook, the lack of tables detailing the number of whores I can bed depending on my Constitution score or the amount of feed and water required to run a throughbred racing-owlbear breeding ranch (specifically subterranean owlbears from the southwest caves of Hoogivzashiite) means that I have little fuel to boost the dying flame that is my 21st century imagination!"
Fear not, for I can help you out! I have compiled a list of downtime activities below. Please assume that any of these activities that do not have a source labeled can be found in the Basic Rules.
(Disclaimer: NecronPariah also has a 21st Century imagination. Reading his list does not guarantee that you might become more imaginative; in fact, he'll probably drag you down to his level of mental vomiting as you read it it.)
Maintaining a Lifestyle
Anyway, a modest lifestyle costs 1 gp a day for food, clothing, rent, etc. Other lifestyles can be found in the Basic Rules
Crafting Non-Magical Items - Can craft 5gp worth of items per day
Can instead make progress towards a more expensive item. The item takes a number of days to craft equal to one fifth its full listed price in gold peices (aka, its full listed price divided by 5).
Must also find and consume components with a total value equal to half the full listed price
A suit of full plate armor costs 1,500 gp, so it takes 300 days to make and requires materials with a total value of 750 gp
You can find a list of poisons here: http://media.wizards.com/2014/downloads/dnd/DMG_257_8.pdf
You can find a list of Renaissance, Modern, and Futuristic weapons here: http://imgur.com/a/8v3hr
Practicing a Profession
By getting a job, you can maintain a modest lifestyle without having to pay 1 gp a day. The money you earn at your job pays for food, drink, clothing, rent, etc.
Being a member of a powerful organization (guild, temple) lets you earn enough to support a comfortable lifestyle, and proficiency in the Performance skill lets you earn enough for a wealthy lifestyle.
Recuperating
You can use downtime to recover from a debilitating illness, poison, or case of the sniffles.
I can't be bothered to post every bloody bit of rules. Look the mechanics up yourself.
Researching
Training
Build a Stronghold
Carousing
Go get your character shitfaced. Go on. You know they want to. Adventuring is tough work, and they deserve a break.
As in, really tired. http://media.wizards.com/2014/downloads/dnd/DMG_128.pdf
WHAT YOUR CHARACTER WANTS
You've played enough to get so much gold that you have to look at this topic, but you still haven't figured out what your character wants? I can't help you here. You're better off playing vanilla Skyrim on a console or grinding out raids in WoW.
Sorry, that was mean. I was out of line there. I've just been so stressed from work recently.
I've got a holiday coming up - let's go do something together, r/dnd, like we used to when we were dating. Let's renew this relationship, and never fight again.
I love you.
Bitch…
Just kidding. You're beautiful.