Aloha
Many airlines do not charge a baggage fee for a medical bag/device. Check with your airline whether they have a medical bag/device allowance, if it covers incontinence supplies, and if a letter from your doctor is required. If allowed, then pack a bag that contains
only medical items (including bed pads, creams, powders, etc.), and check it. Be prepared to open it for inspection, so don't cheat or you'll pay a baggage fee.
I have flown with plenty of diapers (including extras), CPAP, and wheelchair, without paying a baggage fee for them. Suitcase full of diapers got checked. Wheelchair went underneath. CPAP always carried on (I don't use one anymore). And just enough diapers and clothes in my carryon bag to manage through a few days in case luggage went missing.
A few hints for traveling to Hawaii...
It tends to rain frequently during the summer, so be sure to pack diapers and clothes in large trash bags within your cases. This will keep them keep them dry, in case your luggage is being unloaded during a heavy downpour. Clear trash bags are best as they can be seen through, but white works almost as well. You can then use the trash bags to transport your dirty laundry home, without soiling your case(s). (The red mud of Maui really stains)
Think carefully how you will be managing your incontinence through the day. Schedule, lack of public facilities in remote areas, exposure to water, etc., may require modification to your normal routine.
Think about taking a folding soft case for clothes, incontinence supplies, or both. After using up most or all of your incontinence supplies you can combine the contents of the two cases, fold the unused bag, and put it inside the other for the return trip. You have a luggage fee, but you're dealing with one less suitcase. (I typically take a soft case for diapers.)
Think about taking nesting suitcases. After using up most or all of your incontinence supplies you can nest the cases for the return flight. You have a luggage fee, but you're dealing with one less suitcase.
Or, after using up most or all of your incontinence supplies, you will have a case that can be used for bringing back all your souvenirs! But you will be paying a luggage fee for it.
Maui is not Oahu... it has some nice restaurants, but it is still much more laid back than Honolulu. It's easy to overdress and therefore overpack.
Have a great Vacation!