Essentials to live in Laos

The most essential thing to bring is an open mind. No preconceived ideas and a sense of humor.
Electronics are expensive so I would suggest a good laptop or tablet. Along with plug adaptors.
Mobile phones can be expensive too but it is preferable to buy one here. By shopping around you can find some cheaper ones.
Clothing can be found in the markets at a reasonable price.

A good Lao phrase book is essential too. You may butcher the language whilst trying to speak it, but the locals will appreciate your attempts.

Most essentials are now available in towns in Laos.  Do bring a supply of any medicines you take, especially if these relate to diseases more prevalent in the West; but common medicines (for hypertension etc) are readily available in Vientiane and are much cheaper than in Thailand or some other countries.  While some are 'fake'  (e.g. Viagra), most are just as effective as the 'real thing'.  Apart from alcohol and cigarettes, almost all other things are some 25% more expensive in Thailand, from where most originate.  You can however get a bottle of reasonable French wine at less than you would pay in Thailand.  Be aware of the seasons.  While it is hot and humid almost relentlessly, December to January can grant some chilly days in which a sweater or jacket are welcome, particularly if travelling in the mountains.  And if travelling in the rainy season (June-October) lightweight but waterproof clothing is essential.  You can buy a motor-cyclists plastic 'poncho' on any market here, and of course an umbrella; but if you want something with a bit more class, pack it.  You can get good copies of guides like Lonely Planet and phrase books in Vientiane and some places in Luang Prabang; these are much cheaper than in your home country.  Good maps are also readily available and cheap.  But generally be prepared for the fact that most things will cost you more than you expect in a country which is still 'Least Developed'.