Use a piggybank/moneybox, even if you're an adult.

It may seem childish, but seriously consider getting and using a piggybank/moneybox.

I've had one at all times since I was a teenager, and have continued using them well into my early adulthood.

I hate having a wallet full of small change, so at the end of almost every day I'll dump whatever I have in my wallet into the box. I may even chuck the casual $10 or $20 note in there if I'm feeling adventurous.

I'll usually fill a medium-large sized box up every ~6months, and find anywhere from $400-$600 inside.

I take it all to my local bank branch and deposit it using the coin counting machine. Not sure if they're popular in the US, but you can find them at certain CBA/Westpac branches in AUS.

In the end I perceive this as "free money" because it really wasn't that hard to save up, so it's perfect to invest into Shares or ETFs.