I always do this. After I've filled my carboy, I take what is left in the kettle, usually around 500 ml, and put in in a flask and take it to work and autoclave it. Diluting as neccesary to get the wort around 1.040. Many folks sterilize leftover wort in a pressure cooker for later use.
All the time. After i've collected my desired runnings, i just let the lauter tun drain and get 0.5-1gal of lower gravity wort. Into a gallon ziplock freezer bag it goes, gets frozen, then thawed and boiled when i wanna rocka starter. Simple as can be.