Starting the game
Disc: cycle through gameplay options
Side keys: choose selected option
Note that pressing Up on the disc will occasionally behave like pressing one of the side keys, i.e. it'll choose the current option instead of cycling to the next one. Pressing Down instead avoids this annoying glitch.
Exploring
Disc: move through maze
Top side keys: fire projectile weapon; use item in hand
Bottom-left side key: enter pack mode
Bottom-right side key: enter pack mode
Pack
Disc: move cursor
Top side keys: use selected item; open doors; descend stairs; activate and toggle status display; exit pack mode (by selecting spot #2 in inventory)
Bottom-left side key: drop item on ground (note: doesn't work in some spots in the maze)
Bottom-right side key: select weapon; exit pack mode (by selecting blank spot in inventory)
Battle
Disc: move toward/away from enemy; move cursor when selecting items in pack
Top side keys: swing weapon; use item in pack
Bottom-left side key: open pack to bribe monster with item
Bottom-right side key: open pack to select weapon
The Intellivision keypad is unused in Tower of Doom, with one exception: press 1 and 9 together to pause the game.