The most universal Malian dish is rice with sauce often peanut "tiga diga na," tomato/onion/oil, or leaf/okra based - usually with some fish or meat if purchased or prepared for guests. "To," a gelatinous corn or millet food served with sauce, is another Malian classic, though more a village food than something most tourists would encounter. In the north, couscous is also quite common.
In the largest cities, decent "western" restaurants can be found, charging near western prices. Bamako even has good Chinese, Vietnamese, Italian, Lebanese and more. In smaller places, the standard Malian restaurant serves chicken or beef with fries and/or salad - usually edible and affordable, but boring and not particularly Malian. The better places in the more touristy areas may also have some local specialities. "Street food" is a lot more fun and super cheap - breakfast will be omelet sandwiches, lunch is usually rice with a couple sauces to choose from, and dinner presents many options including beans, spaghetti cooked in oil and a little tomato, potatoes, fried rice, chicken, meatballs, beef kebabs, fish, and salad. You can find little table along the road sides and near transport centers.
Snacks you may find for sale include little cakes especially in bus stations, various fried doughs either sweet or with hot sauce, peanuts, roasted corn if in season, sesame sticks, and frozen juices in little plastic sacks. Fresh fruit is widely available and always delicious. Some of the best are mangoes, papaya, watermelon, guavas, bananas and oranges - the particular selection depends on the season.
Of course, as in any tropical, underdeveloped country, food borne disease is a major concern for the traveler. The main culprits for diarrhea are untreated water especially in rural areas and fruits and vegetables which have not been peeled or soaked in bleach water - salads even in fancy restaurants! are likely to cause problems. You should also be sure any food especially meat is thoroughly cooked - generally more of a problem with Western food in restaurants than with Malian foods which are usually cooked for hours. Drink bottled water, and talk to your doctor about bringing an antibiotic like cipro to treat diarrhea that is severe or does not improve over a couple days.