You're unlikely to have much issue with the carry-on limitations with just one or two small items held in your hands. A cell phone and pair of earphones in your pocket certainly doesn't count toward carry-on baggage limits.
The bigger issue is the need to secure items in the cabin for takeoff and landing. Many airlines (particularly US airlines in my experience) will instruct passengers to stow laptops at this time (as they can become dangerous projectiles in case of an emergency) and specifically state that a seatback pocket is not an acceptable place to store a laptop. Many new seat designs have done away with seatback pockets all together as well. Laptops must be stored under the seat in front of you or in the overhead bin. These are not places I would want to leave a bare laptop (laptops will slide on the plane's carpet). As such, I'd highly recommend at least a small inexpensive laptop sleeve to protect your MacBook.
At security, customs, and immigration, one issue is just physically handling your items; navigating an airport with a bare laptop in hand is somewhat inconvenient (how would you hang on to it while you went to the bathroom for instance?) and makes it easy to accidentally lose something. Quickly handing over your ID and scanning your boarding pass is difficult to do one-handed, and carrying a tray of food while trying to hold your laptop in your armpit can quickly become precarious. Furthermore, security officials are trained to be suspicious of people who do not fit into the normal pattern of travelers, and someone who has no bag and chooses to carry a laptop in his hands is at least a little unusual. It's not that you wouldn't be allowed to travel, but an immigration officer might ask you more questions. At a minimum, the items would need to come out of your pockets at airport security.
Beyond that, there are some additional items I like to carry with me when I travel even if I am checking the bulk of my luggage. Medications, if you take any, should never be checked, as you would have a problem on your hands if your bags are delayed or lost. A change of underwear and a spare t-shirt are a nice backup in cast of lost luggage too, and I generally want basic toiletries for long flights. On a long flight, it's nice to be able to take keys and such out of my pockets for a little more comfort. All those things go inside my bag.
Finally, where's the charger for your MacBook in all this?
In short, while this can work, I can't really understand why you want to do this. There's a reason you don't see people clutching laptops in airports; a small bag or laptop case is the simplest way to carry and protect your items. Most travelers have realized this and so bring one along. How is not using a bag more convenient?