Data

Cmd T
Convert the selected range into a Table Mac
Cmd ;
Insert today's date as a static value Mac
Cmd Shift F
Toggle filters on the selected header row Mac

Editing

Delete
Clear the contents of selected cells
Cmd C
Copy Mac
Cmd X
Cut Mac
F2
Edit the selected cell
Cmd D
Fill down (copy the cell above) Mac
Cmd V
Paste Mac
Cmd Y
Redo Mac
Cmd Z
Undo Mac

File & View

Cmd N
New workbook Mac
Cmd P
Print Mac
Cmd S
Save Mac

Formatting

Cmd B
Bold Mac
Cmd I
Italic Mac
Cmd 1
Open Format Cells dialog Mac
Cmd U
Underline Mac

Formulas

Shift Cmd T
AutoSum Mac
Cmd `
Toggle showing formulas instead of their results Mac

Navigation

Ctrl Home
Jump to cell A1
Ctrl Arrow Key
Jump to the edge of the current data region
Ctrl End
Jump to the last used cell on the sheet
Enter
Move one cell down (or confirm entry and move down)
Tab
Move one cell right (or confirm entry and move right)
Ctrl F
Open Find
F5
Open Go To
Page Up / Page Down
Scroll up or down one screen
Ctrl Page Down
Switch to the next worksheet
Ctrl Page Up
Switch to the previous worksheet