Distribute weight so nothing gets hurt — including your back.
The mistake is filling a large container with one dense category. A tote of books is far heavier than a tote of linens of the same size.
Mix dense with light
Fill the bottom third with the heavy items, then top off with towels, bedding or clothing. You get a full tote at a manageable weight.
Stack and slide
Stack three or four totes together and move them as a set instead of carrying them one at a time. It is faster and much easier on everyone helping.