1 keyless deadbolt w/ finger print scanner. Feels kind James Bond-esque but for all practical purposes is incredibly convenient. I can also check it's status from my phone and lock/unlock it via Bluetooth. Next level laziness!

2 under cabinet lighting. Our house is brand new with nice finishes as is, but adding good under cabinet lighting in the kitchen made it look so much better.

3 supplemental garage lighting. I dabble with woodworking as a hobby and prefer a brightly lit work area (garage). I added a series of 20w 6500k LED strips from Amazon (same ones that I'm using for under cabinet lighting in my kitchen) and hardwired them to the light switch. I basically ha e the sun in my garage now, and it only cost something like $60. I would highly recommend this even if you just use your garage as intended.

4 DIY sprinkler system. My new house didn't come with sod in the backyard and I knew I would want to have a nice yard once sod was installed, but wouldn't want to bother with regular watering. I installed a kit from rainbird that consists of 6 sprinkler heads, all necessary plumbing, and a controller ($130-$140). Install was more work than I expected, but it was well worth it. It's pretty much a set it and forget it system. I liked it so much that I installed another one in my front yard.

There's likely more that I'm forgetting, we actually put quite a bit of work into our house. Especially considering that we picked out all colors/finishes. However, these are the four that I appreciate the most, especially with their marginal expense.