The toon opens with Mickey whistling happily on his way to Minnie's house. An interesting note here is that the tune Mickey whistles is actually "Minnie's Yoo-Hoo", the same song he infamously crooned in 1929's Mickey's Follies. The song served as Mickey's theme song (until what year we have yet to find out) and can be heard at the beginning of most of the Mouse's early toons.
Mickey makes it safely to Minnie's, where he is greeted lovingly by his sweetheart. It appears that the two mice are going out for a peaceful picnic. Before they leave, Minnie asks if she could bring along her "little Rover".
Her Rover turns out to be Pluto, with a name change of course. It's very interesting to me that Pluto, known as Mickey's best pal, began as Minnie's faithful dog. Well, technically Rover was Minnie's dog, so I suppose it's correct to say Pluto has always been Mickey's pet.
Mickey ties Rover up to the bumper of his car, and the trio are off for a relaxing day in the sun (luckily, Rover does not suffer the same fate as the dog in National Lampoon's Vacation).
Mickey and Minnie find a beautiful place to set out their picnic blanket. With the addition of lovely music from Mickey's record player, the pair have a relaxing dance through the woods. Unfortunately, the forest critters decide to have a relaxing lunch at the mice's expense.
One last little thing I'd like to share is this frame comparison from The Picnic and The Chain Gang. Remember how that toon is known for the appearance of the character that would eventually become Pluto? Well there you have it; with a few minor changes, a random bloodhound becomes a named dog with superstar in his future.