the genesis of this particular punch was the fact that mangoes and pineapple were both on sale at safeway. it's not much, as creation myths go, but it is the truth.
first you must get some jars together (or, if you are fancy, get out your pitcher) and then you should cut up some coins of ginger (i just wash it and cut it up with the skin still on). for three largish (like spaghetti sauce jar-sized) jars, i used perhaps 2 inches of ginger root, cut in pretty thin slices. then cut up the pineapple (for instructions on that, see rhubarb-pineapple crumble) and the mango.
mangoes seem to intimidate people sometimes. when i was buying this one, there was an elderly fellow in front of me buying like a dozen of them and he was talking to the cashier about what a pain they were to cut up. apparently he was peeling them first and then trying to cut them, which to me sounds like an exercise in slippery fruit, futility, and sliced fingers. it is much easier to cut them up with the peel still on them, then cut the pieces out of the peel.
mangoes are sort of flat on two sides and if you use a sharp knife and hold the fruit so that the stem is facing up, you can cut down on either side of the pit. these are the larger oval pieces above. then there are just the two smaller side pieces and you're almost done! then just make hatch marks as above, push the skin in so that the flesh goes out as in the bottom part of the picture, and use a small knife to cut the little cubes off. so easy! and it's already cubed for you! i used a whole mango and almost half of a pineapple.
then just put the fruit and ginger in with some gin to soak. i let it soak on the counter for a good couple of hours - this infuses the gin with the fruit flavor and infuses the fruit with the gin. i used about a liter of gin in total - just try to get all of the things evenly distributed, if you are using more than one vessel.
after a couple of hours (and i'm sure it would be fine if it was longer than that), add some soda or similar. i used one bottle of grapefruit italian soda and then added some sparkling water to each glass as it was poured (the picture at top is post-italian soda addition). this made for a not-too-strong and very refreshing summer cooler.
we enjoyed it while picnicking and playing bocce ball, which is the preferred way to enjoy it, but it wouldn't be too bad if you sipped it at a cookout or similar.