My early setup is:
Powdermelon jelly (surprisingly good recovery for the monetary value)
Galaxy sword
Gold or preferrably iridium pickaxe
40-80+ regular bombs (other bombs only if you have them and want to get rid of them)
20-100+ staircases (trade jade for them on Sundays)
Lucky Lunch if you have any
Spicy Eel (can be gained from trading rubies)
Triple Shot Espresso if you plan to run around and look for stuff and the ladder/shaft down, can be excluded if you plan to rely on staircases to look for treasure rooms.
I try to make sure I have a lot of empty space in my backpack for the monster drops, ores/gems/geodes, and any treasure rooms I come across.