Format Painter, Fill Colour and Border Shortcuts in Excel for Mac

Formatting is where Windows users notice the gaps on a Mac. Some shortcuts carry over cleanly. Others, including Format Painter and fill colour, have no default key.
Quick answer: In Excel for Mac, ⌘⌥0 adds an outline border, ⌘⌥- removes outline borders, ⌘1 opens Format Cells, and ⌘B bolds. Microsoft's Mac list has no default shortcut for Format Painter or fill colour. The Mac Excel Shortcuts app lets you use the Windows sequences for those (such as Alt, H, F, P for Format Painter).
What works natively on Mac
| Action | Windows | Mac |
|---|---|---|
| Open Format Cells | Ctrl+1 | ⌘1 |
| Outline border | Ctrl+Shift+& | ⌘⌥0 |
| Remove outline borders | Ctrl+Shift+_ | ⌘⌥- |
| Bold | Ctrl+B | ⌘B |
Format Cells is the most useful of these. Press ⌘1, and you get tabs for Number, Alignment, Font, Border and Fill. Anything you can do with a mouse in the ribbon you can do here, from the keyboard.

Format Painter
Format Painter copies the formatting of one cell onto others. The paintbrush is on the Home tab, and there is no default keyboard shortcut for it on a Mac.
Click the source cell, click the paintbrush once, then click the destination.
Double-click the paintbrush to keep it active and paint several areas. Press Esc to stop.
For a keyboard-only route, copy the source with ⌘C, then use Paste Special with formats only. See Paste Special on Mac.
Fill colour
There is no default shortcut for fill colour either. Your options:
Format Cells: press ⌘1, go to the Fill tab, and pick a colour.
Home tab: use the paint-bucket button in the ribbon.
Repeat the last colour: after applying a fill, select another cell and use the repeat-action shortcut. See F4 in Excel for Mac.
All borders and other border styles
Excel for Mac natively lists only outline border and remove-outline. For the others (all borders, bottom, top, left, right), use the Borders menu on the Home tab or the Border tab in Format Cells. On Windows these are Alt sequences such as Alt, H, B, A for all borders. Those sequences are what the Mac Excel Shortcuts app brings across. See Windows ribbon sequence keys on Mac for how that works.