It depends upon the planned use of the GPS function. Even on the island, it can be used for activity tracking and to quickly see how far something is if you are planning to walk.

On the topic of what to do, we have unlocked phones so we go with the local SIM card option -- always cheaper for us than any kind of roaming package.

We also get data on Chippie (4 gb for $55 good for 30 days) which is actually cheaper than on a prepaid plan here in Canada.

Another option might be to just remove the SIM card. You should still be able to use data and GPS.