Read. Newspapers, Magazines, Novels. Toronto Public Library has downloadable e-books.
Listen to music.
Meditate. Might be difficult, but possible with the right headphones and music.
Study for that test, exam or something completely new.
Stretch. You can do neck and shoulder exercises without disturbing too many people. Doing chin ups on the handlebars might be frowned upon.
Email. Get a head start by starting off those long work emails you meant to write.
Work. Get some extra work in, impress the boss.
Plan. create lists of things to do when you get home.
Mental exercises. Sudoku. Crosswords.
Meet new people… You will end up annoying most people. Don’t force conversations on people who don’t want to talk to you. But, hey you never know – you might meet someone new.