There's been some interesting sandwich suggestions made in this thread, and most include deli lunch meats that I really like, but no one has mentioned a few old standbys that make a damned satisfying sandwich in a pinch, some that I haven't used in a long time until this Pandemic lockdown came along and people started panic buying just about everything that stores had to offer, even processed foods that nobody is supposed to like.
Visit any outdoor forum and you're bound to find a thread on the love / hate relationships that some folks have with canned processed foods like Spam, canned hams, sardines, kippers, corned beef, deviled ham, and such, I really can't remember noticing any shoppers going through the check out with Hormel's Chili (with or without beans), I'll bet a lot of cans of that stuff were dusted off several times before they finely made their way into someone's shopping cart, another canned product that used to be very popular in my area of New England was B&M brand Brown Bread, but most folks under 40 yrs old today don't even know what it is, all that stuff disappeared from the super market shelves overnight.
Most deli's in area markets were closed, all you could get was pre sliced stuff, all basic and not much variety, luckily for me and like many other older New Englanders we keep a pretty well stocked pantry of foods we like for emergencies, we occasionally tap it when needed and restock keeping a pretty good rotation going.
So lately since the deli's aren't open and many packaged sandwich stuff (also foods like hotdogs, bacon, and Oscar Myer products are in short supply, I've been using Spam in place of bacon, and using it in sandwiches, along with other processed canned meat products, while some would argue that that stuff isn't any good for you, It still beats dirt sandwiches, and tastes a whole lot better also.