Prepping ahead of time is a huge help for me. When I can carve out a little time, I chop veggies for whatever meals I have coming up in the next few days. I always make double the grain so I have extra on hand for lunches or another meal. I keep cooked beans ready to go, as well as hard boiled eggs and egg muffins (Google recipes, it's basically scrambled eggs with whatever you want to throw in, cooked in a muffin tin for a quick snack or breakfast.). Double the pancakes and freeze the extra. Same with muffins or waffles.
I make my menu plan around using leftovers and that saves time too.
I have some non-perishable snacks in the van at all times. We pack food a lot so we aren't tempted to stop anywhere.
When we first decided we needed to cut back on dining out, we chose a day of the week and that was eating out day. The kids could see it on the schedule and we all looked forward to it (and honestly enjoyed it a lot more than usual). Now we eat out maybe twice a month, and a lot of the time when we do I end up annoyed that I could have made what we just spent a lot of money on! lol