Alright. In my experiences as coupon guy and as a student of voluntary simplicity I have found several ways to get fast food relatively cheaply
Wait for sales. Naturally some places have sales you just have to find out how to find them. Here in bloomington Dominos has buy one get one free tuesday, mad mushroom has $3.99 for a 14" pizza on tuesdays, ponderosa has $4.99 buffets on sunday if you are a student, etc. The paper is a good way to find sales, so is asking friends, so is looking at the signs when you go into restaurants. $5 buffets and $5 pizzas are easy to find if you look around.
Use coupons. If you can’t get coupons through the local paper, you can buy them on ebay. A sheet of ‘buy one get one free’ coupons for many restaurants is usually only $1-2. I have made good use of these and bought BOGO whoppers, quarter pounders and rallyburgers.
Discount cards. Local schools sometimes sell these. I remember one had large pizzas for $5, and buy one get one free deals at a local hamburge place. I suppose calling the local high school and junior high is a good way to find these cards. Do other organizations sell these?
Often I get those weird “decks” of index card sized coupons and ads in the mail; some of them are usually for two-person fixed price meals at really nice restaurants which might have a limited menu but are a very good deal. Generally quite a step up from Tuesdays at Dominos, though.
Volunteer at a soup kitchen. Restaurants often donate leftovers and volunteers in my experience are welcome to take a meal with the guests.
In addition to the fast food places you mentioned, the fried chicken places would often have sales on family-size meals that would be dinner for a week for me. And I expect the chicken could be frozen for future use, unlike burgers.
Chinese food and real Mexican taquerias are also good values.
True. The local student paper covers those, at least it used to. It had all the sales of the week (who had 15 cent beers and $1 hamburgers on thursday, etc) but they stopped carrying that info.
Fill out the surveys they usually have at tables or at the cash register. There’s a local restaurant here that asks you fill one in and sends you specials through the mail on your family members birthdays, anniversaries, etc.
Be good friends with the wife of a guy who’s heavily involved in the restaurant business and gets discounts on a bunch of restaurants and gets more free samples of stuff from vendors than she knows what to do with.
often buffets have pay per pound take out deals that come out cheaper then paying for the eat in buffet. Yes you get less food but get more then enough for a normal meal.