Depends on the date, flight times, your age, sex, and gonzo scale. If you can carry on a snowboard or short skis you could get an hour or two of skiing right now at Mt Baldy. That's cutting it close if there's rush hour traffic at flight time, but midweek its good in the mountains. Raging Waters waterpark is 17 miles from ONT.

Ontario Mills is a huge outlet mall a few miles away. There are wineries nearby with tasting rooms. Are you just looking for a nice meal?