I used mine to put my Mardi Gras haul in. Held up pretty well considering it was probably well over 200 lbs of stuff.
You can make it easier on yourself if you cinch up those straps as tight as you can stand it. Also, try to load the bag where the heaviest items are going to be high on your back, and bulkier, but lighter items are at the bottom.
That won't replace a dedicated backpack/rucksack, but using the same principles, you'll make your carrying chore a little easier.