Technology!
The Jetpack is a rare item that is immensely helpful in traversing the dungeon. It can be found inside certain shops, as a very rare drop from a crate or by bombing the wall behind the Alien Lord in Area 3. (As with all items, it may also be found buried in random walls, visible only with the Spectacles.)
It cannot be equipped at the same time as a cape; picking one up will automatically drop the other if you have it. Jetpacks bought in shops cost $18,000 plus an additional $2,000 for every level beyond the first, making them the game's second most expensive (and valuable) item after the Ankh.
Functionality
For all intents and purposes, the jetpack replaces the Rope, Spring Shoes, Climbing Gloves and Cape. It allows you to fly upwards in any direction by pressing and holding the jump button in mid-air.
The duration of each 'boost' is limited to a few seconds of thrust. If this runs out during flight, the Spelunker will fall out of the air.
The boost recharges immediately when your feet touch the ground - but not when you grab onto a ledge or a wall with the climbing gloves.
Note that the maximum height reachable with a single jetpack boost is high enough to cause falling damage if you land on or below the level you took off from, so be careful when flying upwards if there is no ledge in sight to land on.
The jetpack does not run out of 'fuel', so can be used infinitely (As long as the boost is allowed to recharge).