I would say shopping at GS on sale days - but we all know that we just spend a lot there
Seriously, avoiding the use of disposable goods (paper plates, paper towels, zip lock bags, etc.) can save quite a bit of money.
Using a single-use product for cleaning saves time, space and funds.
Not using too much of products (such as shampoo!)
Turning things off (such as lights, computers) etc when you leave a room. Unplugging what items you can is even better.
Wearing clothes more than once before washing.
If you are an amazon prime member, then subscribing to items that you use frequently. Band together with family members - you can save as much as 20% on many items.
Check your credit / debit cards and make sure you have not subscribed to a service you no longer use.