This will be a fairly short instructable as there is not much to it.
Items you will need are:
Messenger type bags (found mine at a army/navy surplus store)
Sewing machine (or sew by hand)
Cardboard (optional depending on bag style and prefrence)
Step 1: Bags
Step 2: Measure
Step 3: Sewing
Sew the straps using the chalk lines you created in the last step to the bag that you removed the straps from. When done you should have your bags pretty much done. As seen in the photo for the measure step.
Next i reinforced the bags so they would retain their shape vs just flapping in the wind. Of course this is optional and on some bags would make no sense at all. So on to the next step.
Step 4: Reinforcements
Really all you need to do now is put the bags on the scooter.