I have been on, off, under and run over by the wagon. I feel your pain. In the past three years I have gone from running/biking/paddling adventure races to barely able to finish a 5k and gaining weight. The problem, we all know it when it is happening, we stop putting ourselves first. For me, three teenagers, getting married, taking on three more kids, organizing a nasty custody battle, helping my husband with the restaurant, moving, doing my job all took over my life. I let that happen and the day I decided that I can do all of those things and still put my health first was the beginning of getting my old self back.
It is definitely work to set aside time and follow through with exercise. It is more time consuming to plan and prepare healthy meals and eat snacks throughout the day than to just grab something when hungry. You have to make a conscious decision to do it and then even on the tough days, do something.
for me, it is logging everything I eat and every exercise I do on dailyburn.com. If I can't do my regular exercise, then I find a way to log a couple of shorter ones in there (three 10 minute walks, 20 minutes on my bike, some stretching and weights or bands). I spend a lot of time planning menus and meals and snacks, shopping to ensure it is in the house. Once I have an idea of what I'll eat during the week, I am better able to stick to healthy meals and snacks, even if I am not following the menus I planned out specifically.
When you leave the house, have snacks with you. When you travel, like Critter says, bring healthy foods with you. Carry water, drink water, plan on water. Curbs your appetite, keeps you from drinking things higher in calories and I believe the very act of committing to drinking 80 oz of water a day (or whatever) helps keep you focused on the exercise and good food choices. I have water in my hand, I'm doing something right, don't spoil it by eating that thin mint!
Don't be hard on yourself. If you got up and spent 20 minutes exercising today, that is more than you did yesterday. Be proud of that and shoot for 30 tomorrow.