For the smaller grass strip airfields that primarily cater for private flying, maybe a microlight school etc... I see a good cafe as essential along with a strong and active club. Compton Abbas, Popham and Old Sarum being good examples local to me. They will attract the bikers, classic car owners, families at the weekend etc...
Bigger licensed airfields which have tarmac runways with all the staffing that requires are often part of a bigger business plan. There may be industrial premises, various businesses, maintenance facilities, FTOs, hangarage/parking etc... Thruxton being a good example.
It strikes me that the difficulty lies when an airfield is somewhere between the two - many of the costs but less of the income streams.