I've heard that Long Beach Airport is a pretty small airport with not too much traffic. However, I read on some official site that they advise arriving 2 hours before your flight. For anyone who has actually had experience travelling through LGB, given that I fly out from the airport on a Saturday afternoon, realistically, how long before my flight departure time should I aim to arrive to comfortably make the flight?
This depends on the airline. Every airline's website will tell you "recommended check in times" and you should normally plan to be at the airport by that time.
Since JetBlue currently handles 79% of the traffic out of Long Beach, I looked it up for you on JetBlue's website where it says "We recommend you arrive at the airport at least 90 minutes prior to departure."
Practically, plenty of travelers cut it a lot shorter than that... I usually end up getting to the airport 60 minutes before domestic flights and so far have always gotten away with it. The trouble is it's hard to know in advance when the security line is going to be insanely long. Sometimes you breeze through and there's no line; sometimes there's a 45 minute wait.