Potatoes is a sack that contains between one and ten raw potatoes. Baked potatoes cannot be put in a sack. If a player has an empty sack in their inventory and clicks on it while raw potatoes are also in the inventory, up to ten will be placed in the sack. To remove potatoes from the sack requires right clicking the sack of potatoes and selecting the menu option that removes one potato at a time. Sacks can be bought from many farming stores, such as the one in the chicken farm north-east of Rimmington. A maximum of ten potatoes can be put into a sack. This works the same way with cabbages and onions, except for cabbages from Draynor Manor.
Note that if a player has onions or cabbages in their inventory those items will go into an empty sack before the potatoes. As such it is recommended to 'use' the sack on one potato at which point the player can click on the partially full sack of potatoes to continue filling it.
Members can obtain a lot of (free) potatoes in a relatively short time, without waiting for farming patches, by taking plenty of sacks to any potato field, and filling from there. This method is faster than acquiring from a teak larder within a POH because of the single-click action, although using a POH, the player doesn't have to move any squares like they do in a potato field.
For example, put 18 sacks in your inventory, leaving 10 spaces. Head to the North-Eastern Lumbridge potato field and fill those 10 spaces with spuds. Then click on your first sack and all 10 potatoes will 'fill' the sack and free up the 10 spaces again. Repeat another 17 times until all 18 sacks are full with 10 potatoes each. Don't waste the last few spaces before banking, even with no sack space left, make sure you fill the 10 spaces for the final time so you're actually taking 190 potatoes per trip... 180 in sacks and 10 singles.
To take it a step further, go with 24 sacks leaving just 4 spaces. You will need to fill the same sack more than once, but in total you get to take 244 potatoes per trip.
Potatoes are useful for the Temple Trekking, as players must feed five NPCs with any piece of food to stop them from turning into ghasts in one of the events. However, onions are cheaper. On the other hand, raw potatoes have the advantage of not possibly being accidentally eaten by the player. Note that a ghast can turn an entire sack of potatoes into a piece of rotten food.