thermal printer

Hi, I'm a copywriter and I work a lot out of cafes around the city, on my MacBook Air. Occasionally I need to print stuff out when I'm away from my office printer. But most 'portable' printers I see on the market are the size (and weight) of a couple of housebricks. Not great for a small rucksack. Is it possible to use one of those thermal 'receipt' printers, to print out direct from my MacBook onto a roll of 3" or 4" paper, from a word doc? Would appreciate if anyone knows of any similar very small portable printers fit for that purpose. Thanks in advance.