Two spare changes of clothes, a Pull Up and a nappy on hand is always a good idea at your DD's stage. The suggestion of Pull Ups for the car then changing her into knickers once you've arrived is great too. We did that several times with DD.

They do just seem to 'get it' eventually so try not to let it worry you too much. I found using nappies and Pull Ups when 'I' needed her to really didn't seem to effect DD at all. Sometimes she'd be lazy but once she had really got the whole toilet training thing, she generally found/finds it yukky to go in a nappy or Pull Up. She's just woken me then actually to go for a wee despite having a nappy on.