There are various useful items you can buy from the bot, not all are purchased with just GP and some require quest points or other minigame requirements to purchase.
Every item on this page can be purchase with the following command:
+buy quantity itemName - Quantity is optional
Prices are inflated in comparison to Oldschool RuneScape to act as more of a GP sink on the bot. If your minion is an Ironman, you will get the same prices as on Oldschool RuneScape for most items, which can be viewed here.