Heya!
I commute about an 1hr15 each way to uni. After a while you realise you need a lot less than you would think. Your laptop and charger, just the charging cable for your phone (odds are someone has a plug), a book (or whatever you like doing during your commute). I often find myself using commute time to catch up on readings etc. If you have a tablet you could buy books on there, a little less clunky in the bag. A water bottle is definitetly an essential. I recommend 500-750ml ones as it doesn't add too much weight to your bag. Depending on the size of your bag I would also recommend a travel size umbrella or a foldable raincoat always lingering in your bag. They are honestly lifesavers. A notebook and pen are also must haves personally but that is really a preference. Some cash around £30 pounds hidden away in your bag will definitely be a life saver on occasion, sometimes there might be an issue with your phone, lost card or anyhting (keep it seperate from your wallet). Your wallet, house keys, and student ID are essentials that I'd advise always stay in your bag because they can be misplaced so easily.And a small snack/ protein bar always tucked away never hurts.
These are the essentials that are in my bag for my daily commute.
Hope this is useful.
Logan - Student Ambassador, The London Interdisciplinary School