Flashcards are a great learning resource and there are so many interactive ways to use them! Classification and sorting by themes is a great way to reinforce learning categories.
Role-play is an excellent way to learn too, especially for little ones who love pretending and it's a fun way for them to understand different roles and careers. A doctor's kit is a wonderful idea and perfect for that age group where they're curious and interested in the world around them.
For some added fun, what about a toy cash register and some play money to go with the toy store theme? That way, there's so much scope for creative play and it encourages them to role-play different scenarios too. They could 'sell' you some toys when you pop into their store!