General Method Description

Pineapples are valuable items used for everything from Cooking to making supercompost. It used to be easy to get them in large quantities, but is no longer. You can get 40 free (noted) pineapples per day if you have completed at least the easy portion of the Karamja Achievement Diary, by talking to "Dell Monti" on Brimhaven, and you can also buy 40 per day for 2 gp each in Catherby. But if you want larger amounts, you need to pick them from trees yourself.

There are 5 pineapple plants in the forest just south of Karama, each of which gives 5 pineapples. It takes less than a minute to pick these, but then around 5 minutes and 10 seconds for them to respawn. We can make use of some of this time to do a little trick to save on banking. You can run over to the fruit tree patch in Brimhaven and use the tool leprechaun to note the pineapples for you, effectively making them stackable. Even that only adds about another minute, so this is one of the rare situations in which I describe a method that involves world hopping -- by switching between two or three worlds you can get a decent number of pineapples, without being a "resource hog".

Since you are noting the pineapples there is no need to use a beast of burden; summon a forager instead to try to earn you extra money, bearing in mind that you'll need to periodically bank what it gets and renew the pouch as well. Here I assume the use of a magpie and a Summoning potion dose to renew it each time. When you get to level 96 Summoning, use a pack yak to save some time as you only need to go to the tool leprechaun after two pickings.

Note that the respawn speed for fruit trees seems to be independent of the number of players on the server, so there's no need to try to find full worlds.