Hi, LizRmt:
Aside from avoiding highly-refined/-processed foods, what one eats will depend on what they can tolerate. As people heal, they will often find the ability to include a wider variety of foods.
So, I wouldn't rule out any whole foods, unless they cause an obvious issue for your husband. Going through a strict elimination diet is a great way to find problematic foods, though not everyone may be able to do so.
If you're looking for a healthy alternative to Slim Jims, here's one option:
https://www.nosetotail.org/biltong. They're a bit pricey, but the ingredients are minimal and recognizable. Maybe it's something to occasionally add into the rotation, just for variety.
Finally, if your husband could benefit from a cooler of some sort -- and, you don't want to deal with cubed ice at home, reusable ice packs, or paying for bagged ice -- there are electric coolers that he can carry in his truck that would plug into a 12-volt outlet -- if his truck has such an outlet.
I found a couple on Amazon.com and Walmart.com for under $100. A bit of an investment but you could always sell it later on eBay and recoup part of your money, if you should find you no longer need it. Or, if he tried one for a week or two and didn't find it helpful, you could return it within 30 days and get a refund.
Best of luck.