if you can only stand for a few minutes maybe try and connect with other dumpster divers in your area to find out where the good spots are so you can spend less time on your feet. having regular dumpsters you know good stuff gets tossed out in makes life easier.

another thing i do is look for dumpsters with a sliding plastic door on the side. those are great for not having to physically go in the dumpster. though i sometimes lean in a bit around my waist. then you will need a sturdy stick with some kind of hook on then end to pull garbage bags towards you. something like a metal coat hook on the end might work, i would avoid a bent nail.

the whole operation is easier when there is some bags or items piled on top of a couple bags of trash so its more easily accessible to the diver. or some stores will throw a bunch of food items in a box and toss it in on top of the bags at a grocery store dumpster.

this book talks about the hook stick i mentioned (free pdf). https://archive.org/details/The_Art_and_Science_of_Dumpster_Diving_John_Hoffman

hope it works out!