Although the dictionary and many of the previous threads say "bags", the word I almost always used was "bagsie", which was not a contraction of "bags I": "Bagsie I sit in the front seat". "Bags" was occasionally used, in more 'formal' situations, and sometimes "bag"; the conjugation might at times be somewhat irregular
. It is only really used by children.
Incidentally, the explanation in the dictionary Myridon links to is wrong:
Bags I
sit in the
front seat! (= I said I
wanted to do it first, so I should do it, not you.)
This is present tense, so the meaning is "I am first to say "bags" so I claim the right to do it, not you". "Bag"/"bags"/"bagsie" can only be used where there isn't a prior claim.
