if you want to build endurance running and swimming are the best things for you, and if you actually want to see a difference there is no point pussyfooting around, you have to push yourself to the breaking point every time you train.
as for a decent training diet, cut out the shit from your diet and eat a LOT of the good stuff, eggs ( piss easy to cook, add ginger for taste and don't use ketchup or anything like that) meat again easy to cook, throw a steak in a hot pan (use olive oil, but not alot) for a minute each side if you like it rare, it's not gourmet but it does the job, or put some chicken in a baking tray put in a bit of water, cover with tin foil and leave in the over (180 degrees) for 45 minutes, swap out any white bread you eat for wholemeal, start the day with porridge (if you can stand it use water instead of milk and add a scoop of protein powder if you have any, or some cinnamon if you don't) and stop eating big macs, I mean those things are expensive man, making your own food is so much cheaper and healthier. and
training wise cycle a couple of exercises on chest, shoulders, biceps, triceps, back and abs, you should probably throw in a leg session once in a while too but your endurance training would help there anyway. do 3-4 sets of 8-10 reps if each weight exercise using the maximum weight you can (take a buddy for safety if you can) and then one set on a lower weight and complete to failure.
that's the basics really.
or you could take the Jax option