Highly suggested for shore excursions! I have a fairly large one I use as both my carry on for the plane/ship and then once I empty it out in the cabin use it for on land. Nicely fits your beach accessories, change of clothing, and purchaces. Just like anything when traveling do KEEP an eye on it like anything else! But they do come in handy and I don't travel without mine!!!
We too use a backpack when on shore. It's great for all the things that you'll need for the day and all the purchases you will be making. It also distributes the weight and leaves the hands free for more shopping. You also are not as likely to lay it down and leave it somewhere. Let the men wear it ladies, makes them feel useful.