How strict is Contiki for their luggage? They say its only 20 inches...but you cant fit anything in that especially if you have to carry a seeping bag and towel

Also whats the weather like down in Europe...

sleeping bag doesn't need to fit in suitcase.. don't worry
i just got back from this e horizon and the weather was mixed.. paris it rained.. london it was warm some days but rained too,. the rest were mostly jean /capri weather.. definitely bring one or two sweaters that you can put on later in the night .. have fun!!!!