I wasn’t aware of the Worldwide program with easyJet, although 2 months ago, we flew Norwegian to/from Denver to our connection at London Gatwick Airport, and easyJet to/from Gatwick to Crete, Greece. Booked directly with the airlines, so we had separate bookings.
We did carry-on luggage. Norwegian’s carry-on policy is 10kg for all bags per person, so about 22 lbs. Having a lightweight suitcase is helpful, as the weight of the bag itself can cut into how much you can load inside. EasyJet was just concerned that the suitcase would fit inside their bag template, not how much the bag or its contents weighed.
You can check bags, for an extra fee. We opted to bring dinner with us on the flight to London. Bringing salads with less than 3 oz. of dressing was no problem getting thru TSA security at DIA. They sell food and drinks onboard, too.
EasyJet is far from my favorite airline, but you get what you pay for, and they offered a convenient flight at a convenient time, for a conveniently low fare. Crete was a longer flight, but going to/from Scotland, you can grit your teeth for the short flight, and think about how you can spend the money you’ve saved on your flight.