Can I mix tomato and strawberries in one planter? I was thinking of a tomato plant in the bottom with strawberry plants in the side vents.
That sounds like it could be a very interesting experiment! Keep in mind tomatoes do well in slightly acidic soil but if you use a good quality potting soil both plants will be fine. Some varieties of tomato tend to bush out quite a bit, so choose your plant carefully (Cherry tomatoes are grown quite easily in containers).
I'd be more concerned about the strawberries actually not having enough room, but go ahead and give it a try -- with the proper care, you could end up with fantastic healthy plants! Here are some articles that may also help you: