Everything that applies to all sprites. (eg: position, tex coords, velocity, life, etc.)
I did a test to see if I could do this before I asked. I made two classes, one was Entity and the other was Player, and in the Entity class I created a variable 'public int testInt = 1;'; after that I had Player extend Sprite and then made a constructor method for each class, in both constructors was the statement 'System.out.println(tempInt);'. When I tested the classes by calling both of the constructors they both printed 1 to the console. Because of this I thought that it wouldn't be possible to use a Sprite class for something such as holding all of the variables.
The way that I thought it would work is if Player extended Entity then player would create it's own instances of all of the public variables in the Entity class without me having to specificly create them.