I'm based at Southend. There is a cafe in the terminal, and a couple of flying clubs that do food, but it's not likely to excite a hungry Belgian, Frenchman, etc.
Last time I ate there was at Aviators Flying Club, which is at the runway end of the eastern taxiway, the last building before you get to the Hold for 24.
There is a McDonalds in the "Business Park" at the South-East corner of the airfield if you are really desperate.
I've heard very good things about the Propeller and the Crab & Lobster at Bembridge, but never eaten there (they were both closed the last time I thought about going).