Newbury is a biggish town with lots of shops that were probably open on Good Friday. Depending on what time your crew gets in, smaller shops might not stay open past 4pm. However, big supermarkets definitely will be open - we found a 24hr Tesco near our hotel so were able to stock up. We also filled up with petrol. I'm sure there were other supermarkets open too.
The Tescos we found is at:Pinchington Lane, Newbury, RG14 7HB