What others have said about kicking soda to the curb. I didn't exactly have weight to lose when I stopped drinking it, but I felt better in a really visceral way. That, and replacing it with water helps digestion.
If you've got simple ways to introduce more physical activity into your daily routine, make use of those. If you can walk to work in <30 minutes, walk instead of driving. Take the stairs instead of the elevator. Stuff like that. It won't get you ripped in the way that daily manual labor or gym visits will, but it'll help take the edge off.
But yeah. Problem is, if you can't overpower your own weak will, you're not going to get very far regardless of what you try. Step one is always going to be training yourself to deny backsliding impulses. Step two is figuring out food that's both relatively healthful and enjoyable to eat--salads in particular are a thing where the proper touch makes all the difference, though the same applies to some degree to everything. A bowl of iceberg lettuce with big chunks of tomato and ranch dressing or whatever is gross; a bowl of dark greens with little cherry tomatoes, good olives, olive oil-based dressing, raw mushrooms, turnip slices, a little bit of walnut/tuna/hard-boiled egg is delicious.
Basically:
1. Stop allowing yourself to give up.
2. Figure out how to make it a new, enjoyable reality rather than something horrible you're forcing yourself through.
It's entirely about mindset and willpower (barring medical conditions); once you've convinced yourself that living healthily is what you actually want everything else falls into place neatly as long as you have or know how to find knowledge about exercise, diet, &c.