Hope this isn't too late. Yes there is a place to get milk, bread etc. and a great bakers. You aren't far from the supermarkets in Sheffield on Abbeydale Road.
Bakewell is fab- we love looking at the fish in the river and going up for Welsh Rarebit in the Byways cafe. Chatsworth is great ( not sure about which bits are open now). We took our boys to Eyam and wandered round. Walking is fab at Longshaw and there is a good NT cafe there - you can walk pretty much on the flat if that is necessary.
I'm v jealous of you going to Hathersage - we had a fab week there last summer and I grew up not far from there.
We are having a big family meet up in the next couple of weeks in Hathersage. Does anyone know if there is a supermarket there or at least somewhere you could buy milk and bread?? What is there to do in the area that would appeal to all ages (toddler up to 70s)?