With girls, I think that what helps DD to remember it all the time is twofold:
1. She's had VERY severe reactions when she wasn't eating, wasn't obviously exposed...
2. She wears her epis in a small cross-body bag-- it's part of being dressed to go out of the house, get out of the car, etc. Her phone is in there, her wallet, and her inhaler. That's it, really-- it's not a bulky bag.
The first part is a contributing factor in her never ever having ANY thought that she doesn't need one on her because she won't be electing to take risks... she knows that EVERY outing is a risk for her, period. That second part is critical to actually DOING it, I think; because yeah, if it were a "purse" or a "backpack" it would be easy to forget in the name of not looking like a dork.