From easyJets site....
What is my cabin baggage allowance?
All passengers
ONE cabin bag
Maximum size of 56 x 45 x 25cm including handles and wheels.
easyJet Plus, FLEXI fare, Upfront and Extra Legroom customers
One cabin bag as above
Plus ONE additional small under seat bag (For example a handbag or laptop)
Maximum size of 45 x 36 x 20cm which will need to be placed under the seat in front.