i ride bike/take train to work, and have my personal phone, work phone, work laptop, some other things such as power adapter, and a drink to take along the way (all in the same bag)

the other thing is, even though i mostly program, at work we are always up and about, going for meetings, or offsite etc etc

so for me, being as light as possible helps a great deal... the last gen macbook w/dual core i7 (4 thread w/hyperthreading), 16GB ram and 512GB storage, retina display, and all being less than 1kg is a huge boon