When Jackie and Michael are walking to Ned Devine's house and it is raining, Michael is carrying a black umbrella when the two are on the road. However, when they reach Ned's house, Michael has a different umbrella, which is tan with a brown stripe.
When the lotto man comes to the village the fist time to verify the ticket, Jackie states that he has left the little bag with the ticket in it in the phone booth. However, earlier when Jackie and Michael are making the call to the lotto we see Jackie placing a red bag with the ticket in it on top of the phone, but when they leave the phone booth there is clearly no red bag left behind.
The goof items below may give away important plot points.
When Jackie O'Shea is trying to convince the townspeople to share the winnings, he states that it will be divided into 52 shares. There were 52 tickets purchased, including Ned Devine's, but he's dead, so the winnings would actually be divided 51 ways among those who still live.
Jim Kelly, the Lottery man, is seen standing at the back of the church early on in Ned's funeral. In the next shot, he is still in his car outside the church, having not yet found any of the townspeople.