Toddlers while flying

OK so Wednesday night/ Thursday morning my 2 yo and I are taking a surprise trip to see my brother. I have never flown with an kid before. I have purchased a seat for him and know he has to have his car seat. I plan on using 1 bag for both of us and the stroller as our baggage and checking that at the desk. I want to bring our collapsible wagon to put him, the car seat and backpack in it instead of trying to carry it all and checking the wagon at the gate. Does that sound alright? Also can I bring sippy cup and snacks for him? Like I said I've never done this with a kid before and not sure what's allowed.