I also can't do all carry on. Mostly becaues my crazy, curly hair needs too much product for the new TSA rules!
So I pack all of my race gear: costumes, shoes, socks and undies in my carry on. Then I pack everything else in mmy checked bag. Plenty of room for my purchases going home. I actually have a packing spreadsheet. I have a list of days and outfits and costumes as applicable for the trip. Then I have a checked bag section (lists item and a place to check it off) and a carry on bag section (also with the item and place to check it off). It worked really well last year in keeping me organized.
I also plan to wear race shirts, although I will pack one or two shirts for the beginning of the trip and as a backup in case they don't match any of the Sparkle Skirts or other bottoms that I packed.