Catalina is always cooler than the mainland, and May is a great time to visit the island.
If you have never been there, you MUST take the Inland Tour operated by the Santa Catalina Island Company. We've done that a few times, I think it's like a 4 hour tour of the interior of the island, you'll see bison and other wildlife native to the island. There are 2 departures, one in the morning around 9.30 and one in the afternoon around 1pm. Avalon is a pretty little town, you can rent a gold cart and go round and round and round in circles around town. The Wrigley Memorial/Gardens are also a must-see and that round building you see on all Catalina brochures, the Casino/Theater is interesting too. I think they have 1-hour tours there that cost about $18-$20 each.
Here's a link that I am sure you will find useful:
As for the English goodies, shame on me but I have already eaten all the All-Sorts Liquorice, when the Mrs ain't around, I will raid her Cadbury next!