Combine caramels and 1⁄2 cup milk in bowl and microwave, stirring every minute until smooth
Mix together margarine, cake mixes, and remaining milk. Spread half of batter (or a bit more) on a 12 x 16 jelly roll pan and bake at 350° for 6 minutes.
Remove from oven and evenly sprinkle with chocolate chips. If using nuts sprinkle over. Evenly pour the carmel over. Don't worry about getting all the way to the edge—it spreads. Dot with the remaining batter. Put back in the oven for 16 more minutes. Watch carefully it may overflow; I recommend a piece of aluminum foil on the lower rack. Allow to fully cool before cutting.