I used to do the same thing as Lisa when traveling to local gigs, with the backseat and all.
After I bought the wheeled trunk from BedBath&Beyond, I noticed that the jet pack was about 1/2" too long for the trunk. So I hacksawed the top piece off and drilled a hole in each piece. I inserted a double-screw in the top parts and a sunk a threaded brass piece (my apologies for having the exact names for these parts right now) into the top of the pack.
My top rocket screws down onto the rest of the pack.
One of my nozzles is glued onto the dowel rod with JBWeld - ain't a'goin' nowheres. The other nozzle has a small hole in the end, where I run a long screw into the wood dowel from the outside. I store the nozzles in my boots (visualize 2 boots on a stick), and place them in the trunk.
The pack (MB Mark1 '96) fits in the trunk, sort of diagonally. All my other parts fit in there, and my helmet rides separately in a gym bag, stuffed with my armor vest (minus the plates).