I use a small custom keyboard from Techkeys.us:
Techkeys NineKeyBoard CNC Edition
NineKeyBoard CNC Edition – TechKeys
(no affiliation beyond satisfied customer)
or, if I’ll be fiddling with the feed rate increment a lot I’ll load a keyboard remapping utility and use a game pad:
Some folks use a game controller:
Using a Game Controller with CM513 and later
but this seems vulnerable to the vagaries of the underlying OS — I wouldn’t recommend trying it unless one has such a unit to spare (don’t buy one special).
Note that an official Jog Pendant has since shipped: