In case you also hate video walkthroughs:
* Get into the garden
* Get the groundskeeper wet
These two can be done together. To get into the garden you need the groundskeeper to come outside (and open the gate); you do this by turning on the sprinkler, by using the faucet by the fence at the end of the hose. If you wait until the groundskeeper is near the empty garden bed with the sprinkler in it he will get caught in the water.
* Steal the groundskeeper's keys
At any point when the groundskeeper is bent over, you can sneak up (crouch) on his side and steal his keys. This is probably easiest done by taking something and dropping it for him to pick up.
* Make the groundskeeper wear his sunhat.
It is possible to sneak up on the groundskeeper while he's working in the garden beds and steal his hat. If you take it too far away for him to find it, he'll wear his sun hat instead. Possibly best achieved by uprooting the tulip and letting him replant it. (Stealing lettuce or pumpkins don't cause him to start working in those garden beds.)
(Don't bother trying to knock the hat off the door with the rake like I did.)
* Rake in the lake
Steal the rake. Drag it to the lake.
The rake is in the back of the garden, and you have to crouch to grab it. Use zoom out (RB) to make sure you are avoiding the groundskeeper, because he will catch you and take it back.
* Have a picnic (bring to the picnic blanket: sandwich, apple, pumpkin, carrot, jam, thermos, radio, basket)
The picnic blanket is below and to the right of the garden, by the water. Just below the garden is a bench by the water where you can find an apple, sandwich, and the picnic basket. In the garden, on the groundskeeper's table by the shed, you can find an extra apple, the thermos, and the jam. Pumpkins and carrots need to be picked from the garden beds. The radio is outside the garden fence, near the sprinkler faucet.
* [Bonus]: Make the groundskeeper hammer his thumb
The groundskeeper will eventually start to put up a "no goose allowed" sign at the back of the garden. He'll have a hammer to drive it into the ground, and if you honk while he's on the downswing he'll hit his thumb. He does have two practice swings first, but the windup for the real one is obvious.