The Queens Building is close to the Forum, which houses the Marketplace store selling a range of groceries, stationary, and various other products should you need anything during you time on campus.
Coffee, tea, water and other refreshments will be provided in Queens throughout the symposium, along with a lunch.
If you are arriving at Exeter the night before the symposium or staying on beyond the conference dinner on Saturday night, Exeter city centre is a relatively short walk from the Queens Building (around 25 minutes), where there are a range of chain and independent restaurants and cafes. Some suggestions can be found here: https://www.tripadvisor.co.uk/Restaurants-g186254-Exeter_Devon_England.html
If you want to eat on campus, there are a number of venues open during weekdays and weekends: https://www.exeter.ac.uk/staff/stafflife/eat/