You may be one of those dedicated athlete who does back to back BJJ sessions, or who goes to the gym do weights followed by a run and then stretching. If you are training or working out for anything longer than about 2 and half hours I highly recommend taking an easy and convenient snack with you to literally shove into your mouth as you move onto the next session - regardless if you are hungry or not. Your snack does not have to be fancy, just something that will maintain your blood sugar level and keep your energy up for the next session. Also, by eating something in between, this will keep your metabolism elevated and ensure that your body is more efficient at burning fat rather than storing. Eating too little and going for too long without food is a sure fire way to depress your metabolism so that it processes the calories you consume more slowly and becomes more efficient at storing the calories you do provide. In addition if you train a lot and don't eat regularly, this can compromise your immune system so that you are more likely to get sick.
Here are some very easy, basic snacks to take with you on your training marathons that contain protein, fats and carbs.
1/ Sliced apple and fruit and nut mix.
Half an apple and a handful dried fruit and nut mix is all your need. Make sure to get the mix where the fruit has not be dried with sulphates.
2/ Hard boiled egg with half a banana.
One egg and half a banana should be enough to get your energy levels up without making your feel overly full.)
Any snack will do that contains some sugars which can be broken down by the body easily to provide immediate fuel to the working muscles as well as some protein. The fat keeps things smooth and consistent. These example so some good sources of fat, derived from nuts and the yolk in the egg.