Take moleskin for blisters. Insect repellent won't stop mosquitoes from buzzing around but will inhibit their biting. A day pack is a soft frameless pack that attaches to your shoulders and sometimes includes a hip band or waist belt for support. A good one lasts a lifetime. Thin cotton or nylon bike bags or book bags won't hold up well.
Shoulder pads are essential and get one with a tough covered zipper.
Also, choose tabler buckles over double-o rings. They don't slip and adjust quickly. Be sure any pack you choose comfortably carries water bottles. Nothings worse than walking on feet that burn like hot coals. To avoid blisters, make sure your shoes fit properly.