First mention of the doppelgangers
Robin is wearing the wishbone necklace Lily wore in season one. Zoey is seen with the same one in "Oh Honey". This could be explained by Robin borrowing the necklace from Lily in "Double Date" and by Lily and Marshall selling their stuff online and Zoey buying the necklace before "Oh Honey"
In Jen's grocery bag, there is a pineapple. A pineapple is a running joke in the series from when Ted passed out drunk in the first season and woke up with a pineapple on his nightstand. The running joke is that we never find out where the pineapple came from. Only though deleted scenes was revealed that it came from The Captain.