We have just returned to Australia, from America, with our 4 month old. We had our travel agent book us into bulk head seats on each leg of the flight, they have bassinets which were wonderfully handy for Cait to sleep in or play in safely. We kept a dummy handy, to help her sleep, for her to suck on when taking off or landing, and she had no ear-popping problems...or I breast fed her at those times.
We took hour and a half turns in holding and looking after her, so we each had some quiet time to sleep/read/eat.
We had fantastic air stewards who couldn't do enough for us, holding her, helping us in the bathrooms, walking with her to help her settle...Qantas are wonderful!!
We had only two of her favorite toys, to decrease luggage load, she would get distracted easy enough with us and then if that wasn't enough out would come one toy...and presto she's be asleep again.
We took two-three changes of clothes / per day of travel and that was far too much, she stayed in her comfy PJ's most of the time, we changed her three times in 48hrs (and that was mostly for something to do..she wasn't fussed and didn't get herself dirty at all)
We took our own everthing, nappies,change mat,diaper cream,diaper bags, handwipes for us, buttwipes for her, we also packed some saline nose drops for her and used them every 8 hours as she would get quite dry in the air conditioning...these helped her breath easier and settle quicker.
Our doctor said we could give her a small dose of baby panadol if she became restless, no need for us, but could be handy to have just in case.
We took far too much of our own hand luggage...we each had a bag, try to limit it to one bag for you and one for baby and that's it, as trying to carry Cait, get paperwork out, carry three bags and rush to each departure point got a bit much by the end...oh and we also had a pillow and a laptop to worry about too..crazy.
Hope some of this gives you ideas, Melb will be a piece of cake, you'll be landing before you know it, enjoy it and relax, that's the most helpful part, if you stay relaxed, so will your little one.
PS: If your son is at the stage he likes to pull things open, wrap up his favorite toy(s) or a bit of food that you were going to pack anyway, and each hour let him unwrap one thing, it'll keep him amused for a good 3/4hr each time.