This is a list of interventions which have an extremely high expected value to cost ratio. They do this mainly by:
a) being really cheap to implement,
b) having a reasonably high impact in some lives,
c) having minimal negative effects if they do not work.

We recommend trying any of these that seem like they have a vague chance to be helpful.

Try light mode.
Try dark mode.
For motion sickness, try lowering or raising the frame rate of a game.
Try a sleeping mask, if you have any struggles with not being able to sleep due to lighting.
Try f.lux, blue light filters can be very neat.
Try creatine. Not much of a reason not to.
Try melatonin. Not much of a reason not to.
Get a pill organiser.
Increase the font size of everything.
Get some nasal saline spray.
Get some earplugs.
Get a water bottle and keep it close to yoursef at all times.
Try cold showers.
Try preparing your meals in advance.
Try always using subtitles.
Add a footrest under your desk.
Adjust the height of your monitor.
Try noise-cancelling headphones.
Experiment with browser extensions.
Use the custom search engine feature.
Try watching or listening to things at higher speeds.
Keep a few doses of your meds in your wallet or similar.
Tape over annoying LED lights.
Try a different operating system.
Try self-medicating ADHD with caffeine.
Keep a trash can in every place you need to dispose of trash in.

Related lists. Things you’re allowed to do is our favourite out of these.
Barbell strategies.
Things you’re allowed to do.
How to trade money and time.
Sam Bowman’s things I recommend you buy and use, third edition.
Rob Wiblin’s things I recommend you buy and use.
Arden Koehler’s take.
Arden Koehler’s second take.
Collating widely available time/money trades.