Mana foods in Paia has lots of local and organic groceries. It’s all great stuff, and probably close to where you’re staying, but more pricey than the big supermarkets in Kahului, so you probably don’t want to do all your shopping there.
The airport staff at Kahului have seen it all before so your chances of getting your kit through for free are low. Oceansource has some good reports on flying back to the mainland on United (click on the Windsurfers tab).
If you’re flying to Oahu on Hawaiian for a connecting flight, even on another airline then see if you can get your bags checked though to your destination. You will probably have to pay the $100 charge for one set of gear to Honolulu but might get a better deal on the connecting flight since once the bags are in the luggage system they probably won’t get weighed/inspected again. At the very least it saves you the hassle of dragging your bags around again.
The best tip of all is to make use of the porters at Kahului. These guys work for tips, so $20 here can save you a lot in excess fees and hassle as they are working for you and know how to organise things to get you a good deal. Compared to the normal hassle of getting windsurfing bags through an airport it’s nice to just get the bags out of the van then relax while a porter sorts everything out and takes the bags off your hands.
Lessons are probably the quickest way to progress, and Maui has the conditions to learn pretty much anything. Compared to European centres it’s not cheap, at around $100 per 60 to 90 minute private lesson.
Al West has full on windsurfing vans with racks, $299/wk for the mid age ones, $199/wk for older ones, plus insurance. Not the cheapest option but they are big vans and the racks are great if you have lots of gear.
Kimo’s Rent a Car has mini vans which are fine for 1-2 people plus gear at $140/wk or $500/month including liability insurance.
Others
If you’re staying longer than 6-8 weeks I’d consider renting for a week or so and trying to find a van to buy. It’s a bit of a hassle but can be much cheaper. Craigslist and the noticeboard at Kanaha are good places to look.