The only way I have ever made trail sandwiches work is using bumble bee/starkist/chicken of the sea kit. Keeping bread non-squished in a pack is normally impossible though so I just use the eat out of pouches. The tuna/salmon/whatever pouches are basically default choice for everyone who hikes.
If you are hiking as well as camping keep in mind a full day of hiking will increase your calorie needs by 2000-3000 calories. I usually take a bag of granola to snack on throughout the day and some dried fruit. You can eat healthy on the trail but you want to go totally insane on carbs.
Not even remotely healthy but I also like the cheese & meat sticks that you can find at any convenience store.