Kia orana bearsox, welcome to the forum.
Provided your flight arrives Raro on time (as they have been recently), you should be outside the arrivals hall around 8:00am or before. I suggest you head directly over to the domestic checkin counter to drop luggage before making your way to Punanga Nui market. The market site is near the Avatiu wharf, about 1.5kms from the airport heading towards town. Air Raro checkin staff will be around attending to the earlier 8:00am flight, so hopefully this process will work in your favour. Email Air Raro to enquire if this can be done - email@example.com
You would need to be back at domestic by 10:00am or so. If you are already checked in and have dropped luggage, this time is a little less critical. To get to the market it's probably advisable to prebook a taxi or transport from the airport. This will be more convenient than waiting for the scheduled bus services which arrive at the RSA across the main road from the airport at approximately 10 minutes to the hour.
Either arrange hire a car for a short time from Rarotonga Rentals opposite the airport, or organise an airport transfer service like Tiare Transport to meet you, take you into town and return you to domestic by 10am. Tiare Transport is a small privately owned operator who could likely take you to several shops including CITC Supermarket & Liquor shops in Panama, after the market - firstname.lastname@example.org.
If you don't happen to purchase alll your requirements on Rarotonga, the small shops on Aitutaki stock a limited range of most products albeit at higher prices (for imported foods) than Raro. Also TNM store located near Arutanga wharf on Aitutaki stocks groceries and fresh products, as does Aquila store located towards the Pacific Resort locality of Amuri. Tauono Organic Garden would be another good place to purchase fresh fruits and veg on Aitutaki (located near Etu Moana) in addition to Sonja's excellent homefare at her garden-cafe.
Enjoy your visit. Kia manuia.