mizzles, head for the nearest food court for a wide range of quick cheap street eats with air-con and a semblance of hygience. A few of my favorites are...

• the Big C 4th floor food court on Th. Ratchaprarop (just down the street from Gaysorn), cheap (20-50B) and raucous, all Thai food (the som tam guy is pretty good)
• Food Fusion atop the Robinson Silom, pricier and quieter; they have Italian & Japanese food too, but haven't tried them yet

Basically every department store will have these, although some (eg. MBK, WTC) are a little grotty and hard to use if you don't speak Thai. Note that all food courts have some variation of a coupon system. At Big C you buy a stored-value card in advance, at Food Fusion you charge your purchases to a magical stick and pay on exit.

There are also a whole bunch of essentially Thai fast food places geared for the single diner, although most of the logos are in Thai:

• Yum Saap (big yellow smily logo) does yum (salads), curries etc
• Kuay Tiow Something (still can't read the Thai, but their logo is an easily identifiable hungry rat armed with fork and knife) does dirt-cheap spicy noodles (~20B)
• Nooddi does slightly more expensive noodles of all sorts (~50B) and good drinks too
• Hachiban Ramen does good Japanese ramen soup at decent prices (50-100B)
• S&P bakery-cafe-restaurants have a surprisingly extensive menu (<100B) of good Thai food, portions are tiny though

Feel free to drop me a PM if you're in town next week (Wednesday onward).