A voucher looks more like a plain-paper receipt than the shiny/glossy-paper, colorful coupon does. A voucher is also given out separately or alone. A coupon appears in a newspaper or magazine, which works and appears much like a voucher. The voucher is usually given as a discount article for goods or services at a customer service counter or cashier/checker and is often a consolation/substitution gift for services or goods gone missing. A token used to be a plastic coin used on buses and at video arcades in the place of money for passage or access. Now the word token, unlike voucher and coupon, has expanded its variety of meanings broadly into many generalized nuances and uses. It not only means a symbolic coin but a symbolic gesture or appearance. It can be a symbolic representation of a truth/fact, a sensory impression that evokes a feeling, an action such as a bow or wave of the hand to fulfill a cultural mandate, etc. The key to token is "symbol." The key to voucher and coupon (essentially the same discount article) is "easier access."

more or less. token tends to be made out of plastic rather than paper. Coupon and voucher will be paper. token is used in more unusual situations. coupon is more focused as credits for supermarkets/shops voucher is more focused on credit for failed activities, so you get a voucher from an airline if your flight is delayed to buy food.