How do I do this??

Good suggestions from @SweatLikeDog. Start out with a frozen plastic bottle of unsweetened regular or herb tea as the ice block, or put ice in a sealable plastic container so you can dump the water and add fresh ice later. There are also shelf-stable foods that might not be ideal at room temp, but can be eaten in a pinch. Maybe get some of those as backup. (If you're in the US, Walmart or some similar thing is nearly everywhere, too.)

Also, these days, even most mini-marts (like those in many fuel stops) have reasonably nutrient-dense, calorie-appropriate foods: Fruit, hard-boiled eggs, Greek yogurt, unsweetened tea, basic sandwiches (tuna, turkey, whatever protein on basic bread), etc. Fast-food joints also have foods that can work; it'll help to look online and figure it out ahead of time. (Junior burger, veggie-heavy protein wrap, Taco Bell fresco options (and you can customize at most sites), etc.) Even the truck stop diners tend to have breakfast all day (have some scrambled eggs and the leanest meat option; some even have a "diet plate" thing with cottage cheese and maybe a burger patty, some salad or fruit.)

Will it be the thing that's most tempting in the moment? Sometimes not, but I don't think being on the road is different in that way. Most of us need to make a plan using foods we like OK, maybe even like well, but that wouldn't be our first, most tempting choice if calories were irrelevant.

I'm not trying to be mean here, but honestly the most important first thing is to commit to this goal, and mean it. It isn't impossible, it may not even be as difficult as anticipated once past an initial learning curve. The hard thing is to simply decide that we're going to do it.

But focusing on why it's hard doesn't create progress. The only reason to focus on obstacles is to figure out how to get over, under, around, or otherwise past them. Any other focus is a waste of time and energy. We all have reasons why weight management is hard, it's just different from one person to the next.

Exercise is optional for weight loss. (There have been seriously disabled wheelchair users here who lost weight.) Not doing any exercise just means eating less to get the same weight loss rate: Annoying, not impossible. That said, walking or doing a few minutes of random exercise at stops can go some ways toward getting the blood moving and creating a habit of moving more.

Truly, the benefits from this are worth the effort. You can do it if you choose to do it, I'm quite certain. I'm cheering for you to succeed!