You can add pretty
much any frozen /
fresh fruit or berries here, maybe even along with some herbs (basil, mint, lemon thyme, maybe even
rosemary).
Celery, mushrooms, parsnips, tomatoes, turnips, are all fair game as well as most
fresh herbs like parsley, thyme sprigs, or even
rosemary (although that one will be strong so don't use very
much).