Nice suggestions! here are some of mine.
some of them may have been mentioned on cf2 related post although i don’t remember the post
1)Drunken:It forces you to turn right only or left only if you don’t press anything and you have to press the opposite keys to fix your snake’s curve. So your snake cannot go straight it can only do slaloms for a short period of time! I find it a very diabolic red item (mentioned by @Cube)
2)Invisibility(NINJA): there can be four different items for this 2 red and 2 green but only 2 are more interesting i think. 1 green: it makes your snake’s trail invisible when you take it only for the others and for a short period of time. and maybe a red 1 that all the others can’t see their own snake’s trail, so they can’t see where they’re going making it a mean red item. Maybe the red one makes it a bit complicated.
3)the classic switch from cf2: but maybe switch curves also(randomly) for a round. Now for switching curves i want to suggest something in general gameplay about being able to switch curves each round in competitive games or tourneys in which topic can i write this? (mentioned by @Vizzr)
4)Map Division:an interesting blue item that devides the map into smaller maps during a round ,4 little ones for instance that are independent from each other so when you go through a wall you won’t get to the other side of the whole map
but you’ll ge to the opposite side of the smaller 1 that you are in. youll get your self trapped with 1 or more players and have to duel with them in such a small space. Can be strategic item and can be really interesting in teams too
5)Black hole: instead of the classic closing walls we had in cf2 you can have a black hole or square in the middle expanding till it it eats the whole map!