I plan on using my UK commission free bank card with ATMs in Laos (& Thailand), but is there anything, apart from the visa on arrival, that I would need $ for in preference to local currencies?
Buying smaller amounts of $ in the UK is a bit of a rip off exchange rate these days, so I don't want to buy more than I need & lose more by having to change them again into other currencies. I would rather pay for treks & accommodation in Thai Baht.
Who charges the lowest ATM commission for Kip? Are there any free ones (like Aeon in TL)?
the only time i haven't been charged a commission in laos was when i used traveller's cheques at the lao development bank branches in luang prabang, vientiane, and pakse. otherwise, there is a commission on TCs and as i recall there is a commission for ATM use as well. Rufus will have a better idea on the latest however, so hopefully he'll offer his advice.
as for thailand, my experience is that the ATMs not charging a commission (you mentioned Aeon, i'm familiar with Bank of Ayutthaya doing this as well) tend to give a less favorable exchange rate, so depending on how much cash you are withdrawing, you may be better off overall paying the ATM fee anyway.
dollars used to be readily accepted in Laos, but that really isn't the case anymore and i can't think of anything other than the visa on arrival as you've mentioned where you'd need dollars. you should be fine with kip. same is true in Thailand except for maybe at some of the fancy tailor shops or jewelry shops. otherwise, best to pay in baht.
i'd love to hear back from you at the end of your trip to learn how your money management strategy worked out, and what if any fees and commissions you wound up paying. have fun.
There is a 20,000 Kip charge at most banks for a withdrawal of 1,000,000 Kip. The ANZ charges 40,000 Kip but lets you withdraw 2 million.
I would avoid TC. They get charged a commision at most banks. You won't need $ except for the Visa.