I've been using Hammer Nutrition's "Perpetuem" as my sole food intake during the day on backpacking trips for the last several years with good results. It comes in either tubs or 2.5 oz packets(my choice for convenience) of 260 calories. It contains 2 gr of fat, 6 gr of protein, and 54 gr of carbs(complex), plus a bunch of minerals/micro nutrients. The idea is to supply the carbs/protein required to support the metabolism of stored body fat. 2 packets/day works fine for me from mid morning to quitting time in the afternoon. YMMV, but worth a try?? In the evening I use 1st Endurance's Ultragen, a recovery drink that comes in powdered form. 3 oz supplies 320 calories, 60 gr of carbs, 20 gr of protein, 19 vitamins and minerals, and 4.5 gr of branched chain amino acids to help in muscle repair. It has made a noticeable difference in how I feel in the morning, after hard days in particular. Again worth a try, IMO. Hammer Nutrition also makes a recovery drink in powdered form called Recoverite. It has a similar nutrient profile, but I couldn't stand the taste. Lots of others out there as well. Check 'em out, experiment, and I'm sure you'll find something that works for you. One parting thought: If you know any tri-athletes or tri-athlete gear shops, ask them. Those guys practically live of these kinds of drinks when on the move. Good luck!