I usually start Mod/Mod ...but I carry a pair of Skeet, a pair of IC and an Imp Mod and a Full ...in my vest / or on my Rugged Gear cart ...in a fishing lure box. I used to change chokes a lot ...but these days ...only when its necessary / and these days 99% of the time I'm just shooting for fun ...not many registered tournaments anymore ( my eyesight is shot ..! ) ...
But it depends on the course .../and the target presentation.
I carry 5 boxes of 8's, usually a box of 9's and a box of 7 1/2's ...as a rule ( everything loaded to 1oz at around 1225 fps in 12ga ). If I choose to shoot my 20ga --- I drop to 7/8oz loads - but with the same mix of sizes.