Rory buys Dean a wedding gift after being invited to his wedding last minute. She had already given him a catalog and told him to pick a gift with Lindsey and she would order it. She shouldn't have to buy another gift now.
When Kirk calls Lorelai to tell her Lane is in the garage they pan over the band and Gil is standing with them but he doesn't audition and join the band until S4,E7.
When Dean and his friends enter Luke's Diner during Dean's bachelor party, Dean's friend Kyle is wearing a Navy uniform. According to his uniform, he is a Petty Officer 2nd class with 8 years of service. Since he is schoolmates with Dean and had just graduated high school a few months prior, it is impossible for him to have been in the military longer than a few months.
When Lane is going to open the wardrobe doors and the boys come out, the boom arm is visible in the mirror on the left side of the wardrobe.
Rory tells Dean she is in Stars Hollow because she ran out of clean clothes and quarters, indicating she needed quarters to wash her clothes at Yale. However at orientation, the students were told their student IDs operated the laundry machines, so she shouldn't need quarters to wash her clothes.