What can I purchase with $100 that will be the best thing I can buy to make my life better?

I've decided to budget some regular money to improving my life each month. I'd like to start with low hanging fruit for obvious reasons - but when I sat down to think of improvements, I found myself thinking of the same old things I'd already been planning to do anyway... and I'd like out of that rut.

Constraints/more info:

1. be concrete. I know - "spend money on experiences" is a good idea - but what experiences are the best option to purchase *first*
2. "better" is deliberately left vague - choose how you would define it, so that I'm not constrained just by ways of "being better" that I'd have thought of myself.
3. please assume that I have all my basic needs met (eg food, clothing, shelter) and that I have budgeted separately for things like investing for my financial future and for charity.
4. apart from the above, assume nothing - Especially don't try and tailor solutions to anything you might know and/or guess about me specifically, because I think this would be a useful resource for others who might have just begun.
5. don't constrain yourself to exactly $100 - I could buy 2-3 things for that, or I could save up over a couple of months and buy something more expensive... I picked $100 because it's a round number and easy to imagine.
6. it's ok to add "dumb" things - they can help spur great ideas, or just get rid of an elephant in the room.
7. try thinking of your top-ten before reading any comments, in order not to bias your initial thinking. Then come back and add ten more once you've been inspired by what everyone else came up with.

Background:

This is a question I recently posed to my local Less Wrong group and we came up with a few good ideas, so I thought I'd share the discussion with the wider community and see what we can come up with. I'll add the list we came up with later on in the comments...

It'd be great to have a repository of low-hanging fruit for things that can be solved with (relatively affordable) amounts of money. I'd personally like to go through the list - look at candidates that sound like they'd be really useful to me and then make a prioritised list of what to work on first.