so i ended up making a vanguard unit out of my left over marines but i didn't have jump packs for them, so i set about making them. I have for you here a short tutorial of how to make your own:
Materials:

a papermate ball-point pen, its cap, some plasticard and of course...

your marine
Step 1:

probably the most important step, REMOVE THE INK!
Step 2:

slice off the bottom nub of the pen about 3/4 the way up
Step 3:

slice off the top of the cap about half way in the middle
Step 4:

line up the pieces like they would be if they were still attached to the pen and insert the bottom into the cap so you get something like this:

Step 5:

take the plasticard and cut a small band to fit around the "turbine"
Step 6:

Glue it on and secure it tight (as you can see i used a small binder clip which worked nicely), and you will get something like this:

Repeat the process again for the other side and glue onto either side of your marines old back pack and viola:

one jump pack for your assault marines, or raptors or whatever else, add other decoration as you see fit
and all that for under a dollar a jump pack (with only a mild amount of work), better than buying the bitz any day
C&C as you please