Cruise tips you can trust
They begin around $20 per person and go up to several hundred dollars (for certain helicopter tours).
It's wise to book some shore excursions early because they could be sold out before you board the ship.
The shore excursion list is provided in the packet of information the cruise line mails you a month or so before departure. For earlier intelligence, ask your travel agent when you are booking the cruise. Your agent can usually tell you which ones are available and which are most likely to be sold out early - and can immediately book them for you.
If you are not using a travel agent, visit the cruise line's website. A few list their shore excursions and allow you to book them online.
If you haven't booked by the time you board, promptly go to the ship's department that handles shore excursions. If your choices are sold out, at least your name will be one of the first on the waiting list.
Local tour offices
When you disembark, you will find port-side tour offices (or their touts will find you first). Their tours are usually less expensive than the ship's. However, it's difficult for a stranger who just landed to know which ones are reliable, which ones are not. The premium you pay for a ship-sponsored excursion may be worth it for that reason alone.
Your own tour
Perhaps you will want to explore the port of call on your own, or with a private guide. This gives you the flexibility to visit what you want to see - and at your own pace. A group tour does not give you that liberty.
Missing the boat
If the vehicle of a ship-sanctioned shore excursion breaks down, the captain will hold his ship well beyond its scheduled departure time. If the tour is unsanctioned, the ship might (after a reasonable delay) leave without you - for the sake of the other passengers. This means that you would, at your own expense, have to meet the ship at its next port of call. That could be expensive (because last-minute airline tickets are usually high priced) or unfeasible (because the needed flight was fully booked or non-existent). I don't mean to scare you. I just want you to be aware of that possibility.
You can order a free box lunch from your waiter the night before to take on your tour. It will be ready for you in the morning.
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