Yes, it is possible to wild camp on Coast to Coast within reasonable means, such as seeking permission from the landowner, however, that is not always possible. The Lakes section will gives the best opportunity to wild camp, that is high above the intake wall, such places are on the cols, passes, ridges and tarns. As you progress to the Yorkshire Dales and Moors, wild camping opportunities becomes more difficult to find, but there are few places to find the odd sheltered spot out of the way of prying eyes. One area is a no-go for wild camping and that is the Vale of Mowbray, the section between Richmond and Ingleby Cross, that is almost agricultural land. However at that there is camping sites, which charge reasonable prices around about a fiver. In fact, the whole of the Coast to Coast walk does offer excellent campsites, so really no need to wild camp, but that is a personal option.
Tesco or Sainsburys, probably no. However, the major towns on the Coast to Coast are Kirkby Stephen and Richmond, offer the likes of Co-op and the odd independent grocery shop such as Spar, Nisa and Martin McColls. Other small towns/villages on the Coast to Coast are Cleator, Grasmere, Patterdale, Shap, Orton, Reeth, Swainby (off route) Glaisdale, Grosmont and Robin Hoods Bay. These offer the odd grocery shop, butchers and post office, who will sell you basic provisions like eggs, milk, bread and some offer a good range of groceries and other goodies. So, really there is no worry about getting your food or drink. The only thing, you need to know, is the section between Ingleby Cross and Grosmont does have no shop on that section (apart from Swainby, a little off-route at Huthwaite Green) But saying that, hopefully the Lord Stones Cafe will reopen in August and there is of cause the Lion Inn, which does offers excellent meals and beers.
Maps, well, believe me, a guidebook or a footprint strip map (west & east) would be more than ideal and a compass too. There are a few good guide books with maps included and when I did my first Coast to Coast walk in 1990, I used the Wainwrights, "A Coast to Coast Walk" guidebook and that was good enough to navigate with. There is a couple of tricky bits, such as Loft Beck, Greenup Edge, Boredale Hause, Nine Standards, which in misty conditions take some navigating. I think Martin Wainwright's Coast to Coast guidebook is a good one to carry. On my last three crossings, I used the footprint strip maps, which has plenty of detail. There is the Harvey's strip maps and these can be used with a gps.