There are only a few cases in the Community Center bundles where you need more than one of something:
Construction Bundle (all 4)
99 Wood
99 Wood
99 Stone
10 Hardwood
Quality Crops Bundle (all 4)
5 gold-star Parsnips
5 gold-star Melons
5 gold-star Pumpkins
5 gold-star Corn
Adventurer's Bundle (any 2)
99 Slime
10 Bat Wings
1 Solar Essence
1 Void Essence
Fodder Bundle (all 3)
10 Hay
10 Wheat
3 Apples
Other than those, every other bundle only requires one of each thing.
So with the above exceptions, you can guarantee you'll be able to complete any bundle by just holding onto one copy of anything you happen to produce (crop, artisanal good, caught fish, etc.).
Not every single unique thing will be needed in a bundle, of course; but since food doesn't rot or spoil, you can always sell your excess later after the bundles are completed.
Of course, you might want to hold onto two of each thing, so you have one for Community Center bundles and one for any quest that might come up.
It takes two days to upgrade the watering can. Since you can use the watering can both on the day you take it into the shop and the day you pick it up, there's normally only one day that you won't be able to water your plants. So you want to ensure you don't need to water your plants that day. There are a few easy ways to ensure this without having to resort installing a bunch of sprinklers.
- Upgrade the watering can on a day when the weather forecast for the next day is for rain
- Upgrade it on Spring 27, Fall 27 or Winter 27. You don't need to water your plants on the 28th day of these months because none of your plants will survive the change in seasons. Summer is an exception because corn will survive into Fall.
- Upgrade it on any day in the Winter (except Winter 28) if you're not growing one of the few crops, all Winter forage, that can grow then.
Finally you should also ensure that you'll be able to pick up the watering can on day the it will be available. Clint's store is closed or otherwise inaccessible on most festival days.
I should also I point out I discovered the last problem the hard way. As it turns it out not watering your crops one day isn't the end of the world. None of them died, it just delayed their growth by one day.
Best Answer
Shaking trees will drop a seed if the tree has any that day, or fruit if it is a fruit tree. Similarly, shaking bushes will drop berries if the bush has any that day. Other than that, no, there is no reason to go beat around the bush.