On Patriot Express flights, you'll be served a typical commercial airline meal that is provided free as part of the flight. Alcoholic drinks cost extra. On "normal" military cargo flights, you're normally given the option of purchasing a box lunch for about $4.60 (exact change (cash) is appreciated by the Pax rep although they may accept personal checks or credit cards if the capability exists). The box lunch will usually contain 1-2 sandwiches, a soda, fruit, snack bar and chips (or some combination of all these and more). I used to split a box lunch between two children as there is usually a fair amount of food in one. In addition, there is normally a cooler of water and some small snacks the crew makes available. Wise travelers will be prepared with their own snacks and drinks in case you are not offered the box lunch option or you are rushed on to a flight so be prepared! On Navy flights plan to bring your own food/snacks as they may not have box lunches available.
As far as infant formula, liquids and food please see the SpaceA.net FAQ on Traveling with Children.