Exercise
There's a very good chance that you aren't getting enough excercise.
Everyone is always looking for low-hanging fruit in personal development, and even occasional aerobic excercise works.
It's a very inexpensive way to increase lifespan and quality of life.

Investing
Ideally, your money should be doing something other than sitting in a bank account and losing value to inflation; you can lose it to inflation slightly slower by investing!
You don't need to be a crazy investor to take some of your funds and put it in a retirement account or a long-term fund.
You probably know someone who is really into investing, talk to them and do something with some of the money that is doing nothing.

Vegetarianism/Veganism
Do you value the well-being of animals?
Much of the industry surrounding animal farming is worse than people imagine.
HERE is a brutal documentary going over the horrors of factory farming. (If thats the sort of thing that moves you.)
Supporting these organizations less is a great way to fulfill some of your values. You don't need to go fully vegan to do something.
Here are a few things you can do:
-Eat less animal products.
--Many people find it tricky to change eating habits so you can try:
---Recording everything you eat for a week every few weeks to compare with previous habits.
---Introducing more plant protein into your diet, buy more beans. If your total protein stays consistent, this lowers meat consumption on its own.
-Donate to the animal welfare fund HERE annually to offset any animal suffering you do cause.
--If everyone did this, there would be no more factory farming.

Cryonics
If you're not excited about the idea of dying of old age, Cryonics is worth considering.
The points are already made, so I'll link them here:
-Primer/misconception debunker HERE
-General discussion HERE
-Signup guide HERE