I have found the best way to save money is buy stuff at the store when it's onsale only
Yep. You have to gradually work into it, but once you do, eventually, you'll have enough onhand to not need to buy outside of the sales...and that's a good spot to be in.
One other note, shop multiple stores! Different stores have different incentives. They are banking on you coming in for the deals, but buying other items at full price. But, if you just stick to sales, then go to another store and shop their sales, you will cover a lot more ground in getting items on your list, but all for sale prices.
Often, our rule is BOGO (buy one, get one free) only, or better yet, BOGO with a coupon. While our state doesn't double, we can use a manufacturer coupon and a store coupon together. What most folks don't realize, is that even while BOGO, you are still getting TWO items, so you can use a coupon on EACH item.
There are only a few items we get without a BOGO or coupons, but this is because:
1. They are a necessity (like canned cat or dog food, milk, or eggs, store brand bread)
2. Their everyday price is cheaper than other brands, even with coupons/sales, etc.
Main thing though, ALWAYS check the per oz. price, to see if you are really getting a deal (if on sale, you'll have to recalculate this number). Bigger isn't always cheaper.