When leveling your character for a one-shot game, following the instructions in the Player's Handbook.
Then use the following table to see what gold your character should have accumulated at that appropriate level. You can spend the gold on any items in the Player's Handbook and in Dungeon Master's Guide (DMG).
Sadly, the DMG doesn't have prices, so here's a link to the price sheet of magical items: Magical Item Price List
