Complex carbs is what you want so things like, pasta, brown rice, potatoes, porridge, brown bread, beans, lentils and so on If you want fitness for trials then you i don't think that doing long distance running or cycling would be most appropriate as a section is only going to last 5 mins or so and you will have a good few minutes rest inbetween each section. I think that circuit training would be good, you want to have different stations were you do a different exercise such as press ups, sit-ups, squats, burpees etc, how many stations you want and how many times to do each exercise is up to you . Sprint to each station and do that exercise as fast as you can, after one full lap have a break until you feel your ready to do another lap and then just repeat. Each week you can then lower the rest intervals, or the number of laps you do etc Fartlek training would also be useful, if there is a football field near you then use that. Jog around the whole pitch then when you get back to the beginning sprint one length and jog the other three, then sprint 2 sides and jog 2, keep doing this until you sprint around the whole pitch. You want to be doing it 2 to 3 times a week if you want to progress and should be doing for longer than 20 minutes a session.