Can i take a rucksack in hand luggage loL?

If it's of a reasonable size then yes you can take it as handluggage. They will usually have size guides for hand luggage, to see if you can put your bag in that and have it fit. However, when I travel, I usually ignore these, and think: would it fit in the overhead storage compartment along with some other peoples handluggage? Or can I fit it right under the chair infront of me without having any of it sticking out? If the answer to any of those is no, then your handluggage is most probably too big and will need to become luggage in the hold.