Sorry, I think I misread your question...you asked about the best networks for your journey to the Lao border from Kunming. I am assuming that you also want to catch up on emails etc. in Laos so follow my advice as indicated above for Laos.

In terms of rural Yunnan, I don't think there should be a problem with coverage for any of the major carriers provided you stay to the main roads (which you will).

@Blade regarding your question about which networks are best for Laos, the answer is: not the Chinese ones. I don't think Chinese carriers offer roaming (my one certainly doesn't) and even if they do, the charges will be incredibly high.

Your best bet is to buy a Lao SIM card in Huay Xai, recharge it and use that. Try Tigo Lao, Beeline (probably the cheapest network) or M phone 3G (I use that one). Alternatively, recharge your Thai SIM and pay the exorbitant roaming charges, but since there is no reason for you not to purchase a Lao SIM, do so. Even if you catch the direct Chiang Mai-Luang Prabang bus, getting off in Luang Nam Tha to catch your onward connection to Kunming via Boten, Mengla or Jinghong (Chiang Rung), the bus will still stop long enough at rest stops along the way where you can surely purchase a Lao SIM card. If you catch any bus starting from Huay Xai, you'll have even less of an excuse not to purchase a SIM card there.

Carrefour also stocks imported yoghurt, but usually only one brand from Germany. Buy that one. Otherwise, try Paul's shop or Metro.

Well since Hong Kong is outside of the mainland and adminstered separately, it's considered to be "outside of China". Consequently, you can go there to obtain another visa to enter China. If you are going to get a "Z" visa, you might have to get a letter stating that you will apply in Hong Kong. On the other hand, being a Chinese territory, there wouldn't be a Chinese consulate there, so probably you'd have to seek the services of a travel agency.

Otherwise, try a consulate or embassy in another country but be sure to specify to the person sending your application, to state that the applicant will apply in a particular city. If not, they might try to use that as an excuse to send you to the country of your citizenship, as absurd as that would be.

I am currently waiting for my Z visa to be processed and had a look at the Chinese Embassy in Bangkok website and printed out the forms, which I've started filling out. I will be applying for my visa at this post. The forms are quite lengthy, but there's nothing unusual about them except for the biographical page and the 6 questions about the status of your visa in Thailand (which is none of the Chinese government's concern and besides, westerners can easily enter Thailand without a visa anyway so I'm not sure why they would ask these sorts of questions; fill them out anyway though).

On the form, a 1 day rush service option is available, so I'd imagine other Chinese posts would also offer such a service. However, the length of time it will take to obtain permission for your company to hire you is what you'll need to wait a while for, not the actual visa processing time, which can be as short as a day.

Unless it's made overseas and has a label in English, forget it.

If you want supplements buy them either back home (or get them shipped to China) or go to Bangkok or Hong Kong.