Stretching and drinking water are ABSOLUTELY essential. Make sure you stretch before your shift, a couple times during your shift, and after your shift. If you notice any particular muscle groups feeling sore or uncomfortable, Google stretches that target those areas.

I worked in the receiving warehouse at Lowe's for a while and the manual labor resulted in a pretty intense adjustment period for my back and legs. But after learning some stretches that specifically targeted those muscles and doing them regularly I improved quickly. After a month or so I was pretty used to it (and shedding extra weight quickly, which also helped).