1.In the episode where Chris gives Leslie an MRI he comments that Leslie has "a great oven" and that she could have triplets if she wanted to, which is foreshadowing Leslie later having triplets.
2.You can actually listen to Ben's playlist "Benji's Cool Times Summer Jamz" here.
3.At the start of the second season, Leslie sets up surveillance in a park to track down who planted marijuana there. Later on in the season Michael Tansley, a former parks director, admitted to planting weed in several community gardens.
4.Jean-Ralphio doesn't grip Ron's hand during a handshake.
5.When Leslie makes Ann 103 scrap books, one of them is just of their first text exchanges.
6.Early on in Anne's pregnancy Chris tells Anne about how their baby is the size of a green olive, they later decide to name their baby Oliver.
7.Leslie's friend Lindsay Carlisile Shay left for the rival town Eagleton before the series started, which explains Leslie's different behaviour in the first season.
8.When Jerry and Donna bond over takeout they order from Tom's Bistro
9.The little wooden box that Ben uses to propose is a box that both Ben and Leslie use in past episodes to give each other important gifts.