Hi guys,
Eat something fairly easily digestible an hour or so before your workout so it's not going to sit in your stomach too long. Avoid a big meal. Carbs are best and I like a banana, maybe a yoghurt, a sports drink, a smoothie or shake, not too much protein though as it takes longer to break down than carbs.
After your workout, your metabolism will be raging and you've a 30 minute window to replace the carbs you've used. Your body is like a sponge, utilising the calories you consume and is unlikely to store any of these calories as fat.
Try keeping a banana, carb drink, energy bar, etc with you and eat/drink it whilst you shower and change.
50-100g of carbs is about right, depending on the length, type and intensity of your workout, and whether you're dieting and exercising to lose weight or to build muscle, improve your stamina, etc.
Once you've replaced the carbs, you've a 60-90 minute window after exercise to stock up on protein. Avoid eating protein straight after a workout as your body will simply use it to stock up your energy supplies, rather than use it to repair and build muscle tissue damaged during exercices.
Hope this helps,
Regards,
Marcus