There is lots you can do without a gym and equipment....
LUNGES....walking (can carry weights too), backward (standing still step one leg back and lunge down), one-leg squat (back leg raised, balance on front leg, raise up/down), jump squat (in stationary lunge position, jump up, switch legs), stationary (best with weights)
PUSHUPS..... regular, on knees, legs raised, upper body raised
PULLUPS....need bar, but can do if you get the bar that goes in a doorway. Pretty cheap and easy to set up.
DIPS....good for triceps. Can do off any bench/chair/coffee table.
Get some rubber bands....$20 for the ones with handles. Can do ANYTHING with them. Overhead Press, Lateral Raise, Row (attach middle to doorknob or around a tree, pull back...mimics seated cable row), Bicep Curl........etc. Can get 2-3 of varying tightness.
Cardio...easy since running, jumping rope and walking require very little equipment and the outdoors is free. Also can even spring for a couple exercise videos to do in the house during bad weather. Hell, even get a couple Power Yoga videos and you can do some Yoga at home for a change of pace.
Diet is the hardest to change. I think a 40/40/20 is good - sounds not too restrictive for someone who is used to "junk".
Eating healthier can be really good, it doesn't have to be boring. Experiment with spices, different recipes. Try to keep PROCESSED foods down as low as you can. Eat foods mostly in their "natural" state. The less ingredients the better.