If you take a storage crate through The Dark Brethren, you can nab 1600 cannonballs off of the Flying Dutchman. Also, Lords of the Sea is great for supplies

Sea Forts... Supplies are in excess now more than ever. My crew does one Sea Fort for base food and cannons than regular forts for additional cannons and specials.

Blunders and Fires are an extra bonus when we portal hop with TT4 but usually in excess from normal forts.

@sablearc9885220 said in What is the best way to gather supplies before a long play session?:

i cant find a way to get tons of cannonballs/ wood now that flame heart is gone

Pass by a few small islands until you spot a storage crate. Then use that to visit a couple of forts or fortresses using the crate to empty every barrel. If you clean out a couple of those you should be good to go. It should take 15 to 30 minutes.

Adventure is flooded with supplies now.

sea forts/regular forts/right off the dock they are everywhere and easier than ever to collect

Fleets spawn barrels have higher than usual wood and cannonballs so if you wanna kick it old school you can farm fleet barrels. Fleets are super common right now and always in the same spot.

Pretty much everyone is loaded with supplies now so you can just take them from other ships as well if they aren't very aware or are less skilled than you.

Rowboats (storage chests) and random storage crates are abundant as well. You can find one or the other or both on nearly every island a lot of the time.