Well, we added a rear rack and grocery baskets on my cruiser. The pedals were changed to something more grippy...the plastic ones that came with the bike was too slippery when it or your shoes got wet. Later we replaced the seat for one that allowed long distance riding in more comfort.
Just take your time and enjoy short rides in the beginning. That will help you learn more about your bike and it's characteristics and build up your endurance/fitness levels. You'll find the gears you like to ride in and for most people you will use the middle gears more than the biggest or smallest gear. My S.O. loves to ride my cruiser and go shopping with it. Hopefully you'll find your cruiser just as enjoyable and flexible for most activities and uses. Your LBS should offer free adjustments and you will probably need it when the cables stretch a bit after riding for a month or two. After that, it should be relatively trouble-free and reliable and just require regular maintenance...with the chain cleaning and oiling schedule being the thing you have to do most often.