The garden café is open from Wednesday to Friday and you can enjoy soup of the week with foccaccia, something homebaked or waffles. Sit down in Växthuset (the greenhouse) or in the garden with lots of space between tables. Or take home if you prefer.
The garden might at times be booked for events and then the café will also be closed. A good idea is to take a look at http://vaxholmsbedandbreakfast.se/events/ if you want to make sure it is open when you are planning to visit.