Anything.There is nothing that isn't acceptable to the western palate - the food can be quite spicy, although not excessively so.
Traditional Libyan fare appears to be couscous, kebabs, spicey potatoes, salads, and nothing that you wouldn't find in London.
There are a number of good restaurants. Although very basic by western standards, they do produce good meals. Round the back of the Tibesti Hotel there are some good Turkish restaurants; most of their food is very edible, and the prices are very reasonable.
Generally, service is very slow, so leave a good amount of time to have a meal. There are kebab takeaways if you are in a hurry, but in a hotel you can wait 30 minutes to get a waiter to take your order or bring you a menu. To save time it is often easier to pay for your meal/drinks as they are served, before saving the half-hour wait to get a bill.
The food is generally served a little cooler than you expect - it is generally warm rather than hot, and the chips are worth avoiding as they tend to be rubbery.
