There's plenty for a "not-king" to spend money on. It means having to actually keep track of your gold and your belongings. Not just "I walk into a store and drop a sack on the counter and walk out with me hand picked magic item(s)." 5e does not assume that is possible. It is not part of the construction of the very framework of the system. Period. End.
If you are NOT interested in crafting items, building castles, administering domains and/or raising armies (at least some soldiers needs to gets paid y'all!), then there are prices for food, drink and accommodation, at a variety of luxury levels. Are you scraping by cuz your character is a greedy git and wants to have as much gold on him as possible for some imagined/future "retirement"? Are you living high on the hog? You're not building a castle/stronghold/homebase/hideout? Fine. Where are you sleeping every night you aren't on the road? What are you eating/drinking? There's #1. That's uses gold.
The non-king adventurer still needs to get around. Mounts. They cost...a lot. They need to be fed, watered and housed. That uses gold. Even if you're so uber-kewl to have special mounts (like griffons or dragons) they have some cost associated to their upkeep (hell, your dragon mount might actually insist on getting paid, himself, to add to his own hidden hoard). Carts? Wagons? Wheels break, axles break, they get filled with arrow holes or burned to ash by incoming fireballs. Gotta fix it or get a new one. That uses gold.
Henchmen/hirelings/retainers/trainees/etc... You're the uber-kewlz adventurer. You don't carry yer own stinkin' torch! Who's cooking your meals? Who's oiling your armor? Who's grooming and watering your mounts? You need some "nobody's" [alternately, fun well-developed npc's] to do your grunt work. Maybe a small entourage of low level bodyguard fighters, an advisor cleric or mage or lower level spellcasters to handle the day-to-day ritual casting, a few extra rogues to go set off...er...I mean, search for and disarm traps. "Followers", as we'll collectively call them here, whichever term is used, at least some of them will require payment. They need to be fed, watered, housed and [in most cases] equipped. That uses gold.
When was the last time your had your shield, armor or weapons cleaned up/repaired? You don't have a stronghold. No dwarven weaponsmith on retainer? Gotta find someone with the know how to do it for you. That uses gold. If tracking damage to shields and armor isn't your game-style-thing, fine. Instead of tracking it, it just, one day, is unusable and instead of repair, you need to buy new. Either way, it uses gold.
"Incidentals": Your arrows, your spell components, holy water and oil flasks, iron pitons, more oil and/or candles for the lamps/lanterns, torches, grapple hooks (that you can't always recover), healer's kits, and other equipment that may or may not be crucial or used every day/all the time, but you do -over time- use it up. Stuff's gotta be bought as you continue on the path of the non-king adventurer. Track it, piece by piece, or don't and just say "the monthly 'stuff' bill, assuming no special items, is X much. Deduct it." That uses gold.
So, between what's in the PHB and what it seems will be in the DMG, there is SCADS to spend your gold on.
Now, you will tell us how you don't play "that way" and/or don't want to do any of that. So none of that counts and the system is still faulty -because see my previous post.
The DMG isn't giving you alternate options? Yeah. It is. Crafting items, building castles, and running businesses (and other "downtime" subsystems that I don't remember atm). So yes. The DMG does give you stuff to do with your gold...as the PHB already has.
If none of that is acceptable...what do want people to tell you? Go play the system and way you want to. *shrug* 5e's not going to stop you.
As has been pointed out may times, if 5e's core assumptions are not what you need to have "fun", then change them and play how you want. No one's going to stop you. But you can't then whine that 5e "isn't doing it 'right'" or is somehow a flawed system because when you allowed easily purchasable magic items with set-in-stone prices the game imploded/fell apart/got too OP/nothing was a challenge/etc...etc...ad infinitum. That's not 5e's fault or problem.