I spend a lot of time looking at Unicode, at work and personally, just because I love finding a shape already available by default through my default system fonts instead of adding an image for it.

I've reorganized this post to include the symbols in some categories:

Arrows & shapes

Basic arrows: ← ↑ ↓ →
A heavy chevron I use for my terminal: ❯
Filled squares: ▧ ▤ ▥ (more Geometric Shapes – Wikipedia)
Checkbox, empty and filled, this is called ballot box in Unicode: ☐ ☑ – unfortunately, these are not styled consistently in most typefaces. Here's an alternative one for the empty box ▢ And related to this, the checked box: ☒

Mac specifics

These might not be available on all OSes
Command: ⌘
Alt / option: ⌥
Shift: ⇧
Apple logo: 
Control: ^ (this is just caret, shift + 6)

Unique, misc, esoteric:

☉ Sol, or the Sun. It's also used for solar mass.

☤ Caduceus and ⚚ Herald's staff. I can't believe these are available in Unicode, they're so detailed! They're also used for healthcare related signage nowadays.

℻ You read that right, it's just fax as a symbol in Unicode 🤪. But, while looking this one up, I found out that "fax" is short for facsimile which means to make an exact copy of something.

⅋ Turned ampersand. This makes me uncomfortable.

Now all in H1 sizes! (Yes, the alignment of the Caduceus symbols is a bit off…)

☉ ☤ ⚚ ▧ ▤ ▥ ⅋ ℻

I will post more as I find them. 😁