[malloyd]

It's quite dependent on what is for sale.

I think the best choices for dungeon crawl games of all sorts are the ones that help you not die (that better armor, defensive or healing items, stuff that helps you run away reliably (teleport to the entrance/inn items, lucky charms, or smoke bombs for example) or your resurrection fund) or that end up as levels/character points (i.e. training in games charging for it, access to new spells, or Kromm's points for cash scheme).

Third choice is information about the next dungeon/types of monsters encountered, if there is actually a reliable source for that - there usually isn't but some games, particularly those with a more light novel/computer RPG inspiration may have an Adventurer's Guild library or book room with a usage fee.

Increasing your damage per turn (a better weapon) isn't likely to be wasted, but definitely takes second place to not dying. Utility items have a nasty habit of not paying off because they get lost before you encounter the inconvenience again, though that's arguably just because the GM stops throwing it at you now that you have the item....

Realistically expendables to get around specific obstacles often come to be a major use of funds, but you don't plan for those from the beginning, they'll turn up naturally as play goes on.