eBoy runs the Trading Station, offering contestants and travelers an idiosyncratic mix of dry goods that sadly don't include such things as matches, books, condoms, tampons, razor blades, coffee, tea, and sugar. How on earth we are expected to survive without these basic hygiene products1) is unknown2).
What eBoy does sell however, are things such as Grenades, of the BANG, ZAP and WHOOMPH variety. Other fun3) and easy things for sale are Medkits, Improbability Bombs, Teleporters, Energy Drinks, Ration Packs4), and I'm really not going to list it all here. Seriously, it's just a click for you. Anyway, eBoy is a crafty bugger and he adjusts the prices based on stock and player demand. The sneaky bastard will change prices as you're buying or selling items. He buys any item at 70% value of what he sells it for.
The stock and thus prices vary from Outpost to Outpost, so see what's for sale. You might be able to make a profit playing the old buy/sell game. Some contestants are often seen hunting Supply Crates containing these types of items5), which they sell at the Trading Station. Prices are posted just inside the door.