Hi Annie,
I've not had a beach holiday since starting on the Omnipod Pump but I can't see sand being a problems as the Pods are sealed, as for swimming, the manual does say the Pods can be submerged up to 60mins but it's best to inspect the Pod regularly to check if the adhesive is still secure, so I think the main issue with pro-longed exposure to water is the Pod adhesive rather than the Pod itself.
Over the years on the forum I've seen some pump users say they take a pump break whilst holidaying abroad, so going back to MDI could be an option if you think the exposure to sun will effect your insulin, if in doubt have a chat to someone at Ypsomed who'll advise you further.
Have a great time.