F6 opens the backpack. Then press home to equip. pgUp/PgDn to cycle through the items.

I had a more advanced version which had hotkeys, automatic weapon equipment and a nicer inventory control (A3 did not support arrays - it was like hell scripting this inventory system!), but it never got dfinished and is not in a playable state. So you'll only see the hack'n slay part. The original game was more than that, but I needed something for the contest

Press F1 in the game to get an overview over the key layout.