I'm planning to go from China to Malaysia, Thailand, Cambodia, Vietnam and Laos (and back to China) OVERLAND, in this succession. Well, flight Guilin - Kuala Lumpur and then overland.

All I have now are Chinese RMB and a Visa debit card for ATMs.

This said, what should I do about money before the travel? I know it's not a problem when going by an airplane - one can simply exchange or withdraw some money at the airport. But if we'll be crossing borders overland all the time, I'm afraid that if I didn't already have some cash in the currency of the "next" country already at the border crossing, we could get stuck at the border since we won't be able to pay for the transportation to the next city with an international ATM.

Am I worrying too much?
Should I buy some US Dollars in Kunming to use them at borders (if they are of any use in those border regions)? Or buy (in Kunming), say, 100 or 200 RMB-worth of currencies of all the countries I plan to visit beforehand? I've never traveled in such remote regions through overland crossings, so I really don't know what should I do...

Thank you!

Usually, this isn't too much of a problem.

The reason is because when you try to take transport after crossing the border, the transport operator will usually accept either currency (local or from the country you just came from). This was the case when I crossed from Malaysia to Thailand and Thailand to Cambodia (they preferred USD or Thai baht in Cambodia!). Don't worry, the transport operators at small crossings understand your dilemma! This is in the out of the way border crossings i.e. smaller border crossing posts without a major town around it.

At the major border crossing posts, they will almost always have international ATM's where you can withdraw money and/or they will have money exchange places. Money exchange places on border crossing posts usually give you terrible rates, but sometimes its worth it if you have lots of currency you aren't going to use. But I would advise holding onto the currency until you get to the next big town for better rates!

The last bit of advice - get about $100 in small USD notes (I would advise five $10 notes, six $5 notes and twenty $1 notes. This will cover you in cases on the rare occasion where the above doesn't work (i.e. ATM machine is broken, you cross early/late and buses aren't available - only taxis and they will only take local currency but if you flash USD they will probably accept!). Don't worry if you get to Vietnam and haven't used your USD at all - its a second currency in Vietnam and your accommodation will quote you rates in USD! You will be able to pay for lots of stuff in USD in Vietnam so can use it up.

Thank you very much for the info!

Then I'll just try to exchange some RMB into small USD notes. I hope it's manageable at Chinese banks... (I always die looking at all the unnecessary bureaucracy in China).

blobbles has pretty much covered it, but a couple of additions:

CNY is relatively easy to change in Thailand.

Large denomination USD in Thailand will get you a better rate, so if you're in Thailand a while, pack some Benjamins.

Bank of China will sort you out with USD.

Have a good trip!