Spice in the Sky is a job in Sly 2: Band of Thieves. In order to destroy the locks on the cabooses of Jean Bison's iron horse trains, Sly must take to the skies and gather several tanks of unstable spice gas.
After the briefing, Sly will automatically jump onto the plane and Murray will fly him up to where the balloons are. Once Sly jumps off the plane, activate the paraglider and glide over to a balloon. Landing on one will pop the balloon and boost you up, allowing you to land on another; at the same time, the vacuum backpack will collect the spice gas from the balloon. A balloon does not need to be hit directly to be popped; if it is hit from the side or even the bottom, it will still give a boost up.
In order to fill the backpack, you must pop five balloons. You will know it is full when it glows green, upon which you should paraglide over to one of the three trains' cabooses (marked with red targets) and blow off its lock. Once the first lock has been blown off, return to the plane and repeat the process twice more. The job is complete once all the locks have been blown off the hatches.