The South East part of the Zoo (close to where the bears are located) has public BBQ's and picnic tables. The perfect way for me to end a day in the Zoo is to take my own drinks and sausages with me, and then sit down either on the rocks or on the pickic tables and eat while admiring the beautiful Baltic Sea.
It can be quite expensive to eat in the Zoo restaurants, especially with the entrance fee, so this offers a great alternative when you get hungry! It's not a big Zoo, so carrying food and drinks around won't exhaust you. To avoid crowds at the picnic, try to visit later in the afternoon.
You can buy coals from a few restaurants close by, but if you are lucky, you might be able to use someone's leftover coals that are still hot!