I believe anything that you put in a container is safe and kept until the end of the game. Just dont put items in Baldur's Gate since it changes on one part of the game. Any container in Beregost is safe tho. Atleast That's what i did in my playthroughs.

Thanks, I will try it.

Plot-relevant (i.e. unsellable) items won't disappear even if they're on the ground, but it's more convenient to put them into a container or several containers for organization. Beregost and the Friendly Arms are good choices because of their central location. Friendly Arms doesn't have a huge amount of storage space, though, but really you only actually need one container.

I find the best place to store things is in Beregost. If you enter the map from the south (zero travel time), you will appear at the entrance to the Jovial Juggler. A few steps to your left is a barrel where you can put things.

The fact that the town is centrally located in the region, the barrel is right near an inn, and most importantly, it's right next to an entrance spot on a map means you can very quickly enter the map, give/take what you need with the barrel, and be back on your way in no time. The FAI and other maps require you to spend time travelling in to get to a container, and then more time travelling back to the edge. The barrel by the JJ is ideal. Plus, there's two more a little further on if you want to sort for some reason.

The JJ barrel is the best place to store things.