Maintaining a Lifestyle
If you don’t want to get a job, you must spend your accumulated wealth on day-to-day living.
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: link
Practicing a Profession
By getting a job and contributing to society instead of mooching off it, 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.
Proficiency in the Performance skill lets you earn more to support a wealthy lifestyle.
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.
Go to the library and read a book (nerd), or gather rumors at the local pub. The DM determines whether the info you seek is available, how long it takes to find it, and if you have to make any ability checks.
Educate yourself! Become proficient with a new language or set of tools with this new 250-day course! For the low, low price of 250 gold, you too can perfectly imitate dying cats on a set of bagpipes, or speak to the only gnome left in existence after your party killed all the others!
Build a Stronghold
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. link
Crafting Magical Items
Only if your DM says so and has shelled out money for the DMG because they truly love you (as opposed to tolerating you because you’re the only group they can find, and let’s be honest, this is far more likely).
May require so much work to get the materials that it isn’t worth it. That’s your problem for trying to make your magic items the honest way instead of murdering a defenseless dragon and stealing them.
Selling Magical Items
Imagine you find a genuine Da Vinci painting that makes the Mona Lisa look like a crayon drawing. Now imagine trying to sell it while communicating only by post and 100,000-a-minute phone calls. Imagine trying to convince people it’s a real work by Da Vinci. Imagine finding someone who’s willing to buy it and can actually pay full price. Good luck.
WHAT YOUR CHARACTER WANT
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.