With 7 kids, the only restaurants our parent went to as a family were Chinese restaurants. Maybe that is a factor in me marrying DW, who loves chinese food.
Hand-me-down clothes. I was the third son, so at least half my wardrobe was from my older brothers. When My siblings and I married and started having kids we would pass infant clothes among each other like this.
We drank lots of kool aid. The little packets into water and then add probably too much sugar. I do sometimes use the little sugar free "single serve" koolaid packs.
We ate a lot of liver in the home, as that was the cheapest cut of beef. As an adult I do not eat liver. However, given its health attributes, that may have contributed to me and my siblings rarely getting sick growing up.
Mom would reuse lipton tea bags to their limit. That habit I finally stopped 10-15 years ago. I mainly drink decaf tea and have "graduated" to fancier english breakfast brands

. But as times it still feels a little strange to throw out a tea bag after one use.
We had a washboard that was used if you only had to clean a few things. While not cheaper, we went to laundromats to wash clothes until I was 13, when our parents first purchased a washing machine (2 years after we moved into our first house).
Clothes were dried by hanging them on clotheslines or putting them o the radiator. I still find it interesting that none of us suffered burns from being around hot, exposed radiators when young. We have a dryer now, but we do have indoor clothes drying racks that are used mainly by DW.
Saving bacon grease. I do this, but only to fill up one bottle. It makes my bacon caramelized onion dip oh so delicious

.
Many empty glass jars because drinking glasses. We rarely save them these days, like the one of use for the bacon grease.
One pair of sneakers, worn until a hole appeared. Then put in a couple of pieces of cardboard until the next birthday or Christmas, and you knew what present you would get. Now I have 6 pairs of sneakers, blow that dough!
Adding water to ketchup and mustard to make sure we used every last drop of those condiments. I will do this these days if (a) we are eating something that I want to put those condiments on, (b) practically empty bottles are all that is left in the house because we forgot to stock up, and (c) I am too lazy to drive 5 minutes to the store to buy a new bottle.
Many more I can think of. But in truth, at the time, we did not think of these things as cheap, that was normal to us.