Арбус & Квас
How do you know it's summer in Kiev (besides the calendar or the temperature, smartass)? Well, just look on the street. At the beginning of summer, Kvas vendors will appear. They're the people dispensing drinks from these tanker looking things, as on the right in that picture, selling the surprisingly good drink that's basically made from fermenting bread.
When the dog days arrive, you start seeing these large cages appearing on the street. Shortly thereafter, said cages will be filled with watermelons, as on the left in that picture. The melons here are so good. Very sweet and they actually taste like watermelon...unlike the watered down flavorless things I've grown used to in the states. They're quite cheap too. A whole melon will go for about two bucks or less. Consequently, I've been eating watermelon every day for the past week or so. Come mid-September, they'll be gone.