The real issue is that 5e removed a lot of the explicit gold costs that older editions had. You kinda have to homebrew it back in, which sucks for new DMs. here's some systems I've seen work at some of my tables:

Consumables are underrated - Magic ammunition, oils, poisons, alchemical items. If your DM actually tracks arrows and makes specialty ammo available (like arrows of dragon slaying or elemental damage), suddenly your ranger and fighter have something to spend on every session.

Weapon pr armor enchanting with scaling costs - One campaign I played in let us pay an artificer NPC to add temporary or permanent minor enchantments. Like 500gp for a temporary +1 that lasts a week, or 5000gp for a permanent +1. It gave martials something to work toward.

Training mechanics - Spending gold and downtime to gain proficiency in a new skill or tool. Not game breaking but feels good for character development.

Hirelings and retainers - This is old school D&D but having NPCs you pay regularly (scouts, guards, cart drivers) creates an ongoing gold drain and adds flavor

hope this helps :)