...I don't think his IPAD has a lot of storage, but an external hard drive or additional cards may be the answer.
As others have mentioned, there are inexpensive little card-reader gizmos you can plug into your iPad, which allow you to easily copy photos to the iPad. But then you're limited by how much space your iPad has - you will need to take a hard look at how much available space you expect to have there to determine if that's a realistic option.
BTW, you generally can't easily hook up an external drive or other external storage device to an iPad.
A bunch of extra cards might cover you. It's certainly a simple solution.
he takes a lot of photos, so maybe increasing cloud storage would work.....
You should carefully evaluate exactly how much data (how many images, how large they will be) he's really going to need. It could be a lot more than you think (depends on the camera and the photographer).
Cloud storage may work OK in some cases, but if (as I suspect) you would be at the mercy of whatever free wifi your hotel offers, beware that this may not be a realistic option. Hotel wifi speeds may be fine for email or social media, but if you need to push large numbers of large images (very common with today's cameras and some photographers) that may far exceed your ability (or your patience).
As an (admittedly extreme) example, I came back from a trip to Italy last fall with over 14,000 photos, average size was about 24 megabytes. That could take a lifetime to upload to a cloud service from a slow hotel wifi connection.
There are photo backup devices you can buy (basically a hard drive in a case with a card reader built in and a simple operating system) that can work (I have had several over the years and currently travel with one, with a 500 Gigabyte capacity) but they can get expensive, and they're one more electronic gizmo to carry along (and hopefully not break or be stolen).
For many of us, photos are our most precious travel souvenirs, so having a reliable backup is important. The best solution for you really depends on what your storage needs are, so the best way to start is to figure that out.
Hope that helps.