It's a really long bus ride (maybe 30 minutes), but I have never done it. Maybe @Astro Flyerwould know. There might even be a senior fare. If you do this, give yourself PLENTY of time to get back to the ship.
Guri Guri has the small bags (not cheap). Foodland is suppose to carry them. You would think they would be in every store...not. They don't have a long shelf life (eat now). Greasy, crunchy, so good/so bad for you.
https://www.mauicounty.gov/609/Maui-Bus-Public-Transit-System
Looks like you can get the bus near the harbor (sample)
https://www.rome2rio.com/map/Kahului/Maui-Ocean-Center#r/Line-29-bus
Editted: Looks like an hour each way. Plug in your date and time.
https://www.google.com/maps/place/Kahului+Harbor/@20.8515868,-156.5763686,12z/data=!4m27!1m20!4m19!1m6!1m2!1s0x7954d32ec1dbca0b:0x9bec5dc1d580588!2sKahului+Harbor,+VGXF%2BQV,+Kahului,+HI+96732!2m2!1d-156.4752777!2d20.8994444!1m6!1m2!1s0x7954d130a0c031b3:0xad1cd589958ba5c8!2sMaui+Ocean+Center,+The+Aquarium+of+Hawaii,+Maalaea+Road,+Wailuku,+HI!2m2!1d-156.5121616!2d20.7926322!2m3!6e0!7e2!8j1713519000!3e3!3m5!1s0x7954d32ec1dbca0b:0x9bec5dc1d580588!8m2!3d20.8994444!4d-156.4752777!16s%2Fg%2F11txjns95m?entry=ttu