Like elsewhere in England, Oxford has seen a flight of cafes and delis, particularly targeting the city’s large student population. The Covered Market in the center of town hosts several such cafes. The falafel is very good in Organic Deli Café & Whole Foods Store (sadly, the same cannot be said about much of the rest of the menu).
For good Thai food, go to Chiang Mai Kitchen. This one is set in an old 16th-century building in an alley behind High Street, complete with squeaky wooden floors. Other foreign options include Oli’s Thai and Yeti Nepalese Restaurant (both of them further to the southeast).
Town: All the colleges and sights in the historical center are easily within walking distance. The walks are filled with beautiful old Oxford architecture. Some minor sights, restaurants, or some of the cheaper hotels are located further away (e.g., Park Town in the north or Temple Cowley in the southeast). There are regular buses (cost about $2-$3 per ride).
Taxis are also available but generally expensive. Uber is usually a cheaper option.
Airport/out of town: most people visit Oxford from London. A train ride from Paddington or Marylebone station takes only one hour. Buses are slower but cheaper. Alternatively, Oxford station has good train connections with Birmingham or Southampton. There is an airport just north of Oxford, but commercial flights from there are infrequent.