Food is always a big expense and my grandmother who lived during the depression taught me that if you make up a menu for a full week and had only those meals it saved a lot of money. I still can't let a Wednesday go by without thinking about her meatloaf.
And then when I cook something, like meatloaf, I freeze half and I save some for lunch the following day.
Coupons are mostly a waste of time and money unless they are for something that you use all the time. If you clip and use it because it looks like something you'd like to try, its no bargain. But it never hurts to look.
Propane is another thing you can save money on. I have a slow cooker and I roast veggies in it and use it as much as I can. We don't use the propane heater at night to keep us warm, extra blankets and a small electric heater helps out.
Small short trips instead of long hauls save gas as has been mentioned before.
Where you camp and when also makes a difference. We found that in our state they have discounts for off season camping.