Use a few cool pack and put the chocolate in a insulated bag, It will be fine.
The cargo area at 35,000-40,000 Feet is COLD, very cold! The biggest issue is if the bag sits on the hot tarmac for awhile in the US or Jamaica, That's why I would recommend cool packs and a insulated bag. If you don't use a cool pack/insulated bag you'll face what I did, a bag filled with melted chocolate and ruined clothing lol
The seeds are questionable, If it was me I wouldn't say a word to customs about it. I would stick with heirloom seeds (search Google for more info). I personally see no issue with it but live plants would be a no-no on every level as they could bring diseases into Jamaica that never existed before...hurting agriculture.