I used to have lots around the special tree stumps, I just left them as they looked nice, but the residents didn't like them, they said the town was messy, so I have been harvesting them and eating/selling them and I did notice this last week mushrooms sprouting all over the place so I have been eating/selling them and only realised yesterday that I may need them for harvest festival, so I only have a few, I have done the first meal as I had kept some vinegar from last year, the thing is I don't really have the time for the fishing, on this day there should only be the fish swimming about that you actually need to give to the residents, I caught about ten today and none were what any of my residents wanted, I think that it would be better to have it on a Saturday or Sunday when people have more time.
Just to add that this may have changed with the new update to the game, which I have not yet installed.
I agree to a point, I always try and do the takes, but you are right some of the events you don't get enough time or warning, it's like all the sweets for Halloween I don't have the room to store loads of them, and the same with this with the mushrooms, I knew a event was coming up and knew I needed stuff like vinegar, flour, milk etc but forgot about mushrooms, it has always got me how there is no greengrocer in the game with a shop where you can sell fruits to and then get things from him like milk and flour etc, catching fish for residents that then give you things like butter it way too time consuming, like the first meal I have a round mushroom, a flat one and some vinegar I had over from last year and then was asked for a special ingredient, I had a rare mushroom so gave that but it wasn't right then going to a resident who I had managed to get the right fish for said that for the (whatever the first meal was) the special ingredient is butter which I do not have!!