Probably not the kind of investments you are looking for, but here are a few tips (srry for the lengh, I'm brainstorming here ^^):
-Buy in bulks; there is no point to buy 3 juice boxes for 1,29$ when you can get 50 for 9,99$. Here in Quebec we have Costco and when my kids we're younger I could get diapers at 50% of the price they would sell them elsewhere.
-Don't go to the grocery store when you are hungry, it empedes your jugement on what you really need and you might come back home with half of what you bought being extras.
-Cook: not only will it significantly lower the price tag of what you eat, but you will also eat a lot better. Fastfood is overpriced (wtf McDonalds, it's near 40$ for a family of 4 here (/w 2 children) and there are lots of preserving agents.
-Start a garden: not only is it really usefull to learn how to grow some of your food, but on the long run you can save some money and have a calm hobby far from your computer screen .
-Wait for you games to be out for some months before buying them, you might get them 2/3 or 1/2 of the price and fully patched. I might be biased, because the last 2 games I pre ordered were CoD WW2 and Fallout 76 (bad investments).
-Modify you desktop computer yourself: often, when you only need to change the RAM or your graphic card, you can buy and change all of that yourself. It's really easy to learn, watch some online tutorials (just be carefull to check the dimensions before buying ^^). I built a computer as fast as my friend's for half the price because he wanted to just buy and play.
-Free money doesn't exist if you are not in the 1%; anyone that offers you something that is too good to be true doesn't have your interest at heart, but theirs.
-Buy used: my car costed me 4 500$ 4 years ago and I still have it; my step sister bought a brand new car for 60 000$ and just by taking it out of the garage she lost a huge part of it's value.
-Don't go to the clinic test programs; sure you can get a few hundred bucks (sometimes thousands), but I would say that investing in your health by not challenging it is a wising investment.
-If you are ethically flexible, there is no way you have to pay for porn or TV series when you have the Internet.
-Exercise and keep a good mouth hygiene, your good health can make you save a ton of money.
Hope it helped you guys