In elementary, my kids really only have to tote around their lunches and a thin folder of papers--plus whatever toys they sneak in there to play with at recess!
I think messenger bags usually are too skinny to fit most lunchboxes into comfortably, but that depends on the style you use. Also, if it's possible your child might be able to bike to school, I think the bag slipping around could be troublesome.
For young elementary students, it's important to get the right sized bag. Usually there are preschool, younger kid and older kid versions at the store.
I have seen some nice homemade rucksacks, made of sturdy corduroy and many layers of fabric for the strapping (or leather). The easiest way is probably to have a drawstring top and then perhaps a flap to cover that. However, I think my kids would say a drawstring top is too fiddly and takes too long to get into.
Backpacks are not so bad--they don't all have cartoon characters on them.
