There are a few things you should not travel without:
Most Cambodians dress up casually except when they are attending formal events. It is common to see men and women using Krama, a Long, narrow checked cotton cloth round their neck. The krama is just like a piece of clothe. Lightweight, loose-fitting, cotton clothing is recommended and long-sleeved items should be included for protection from mosquitoes and the sun. During the rainy season an umbrella is more convenient than a rain coast. A jacket may be needed in hotels and restaurants using excessive air-conditioning. A hat and high-factor sun block is advisable as protection against the hot sun when sightseeing. When visiting temples or pagodas, including those of Angkor Wat, shorts and T-shirts are acceptable. Shoes are generally removed at the entrance to pagodas. For visits to the Silver Pagoda, which is within the Royal Palace grounds. visitors are asked to dress more formally. Gentlemen are required to wear long trousers and ladies should wear long trousers or long skirts.
The Riel is the official currency of Cambodia. The bank notes are presently in denomination of 50, 100, 500, 1000, 5000, 10,000, 50,000 and 100,000, but the 500 and the 1000 riel notes are the most commonly used. There has been some devaluation of Cambodia Riel in the past few years rate of exchange, in November, 2010 is approximately 4100 Riel for a US Dollar.
Most hotels and many restaurants and shops set their prices in US dollars. Small transactions (less than a dollar) are usually done in riel. Always carry some small riel for motorcycle taxis, snacks, beggars and other small purchases.
Other major currencies such as the Euro, Yen, Bath and others can be exchanged at Banks that are located in all major towns. US dollars can be freely spent though travelers are recommended to use smaller denomination. Most places will refuse old, tatty or damaged US bills.
Traveler cheques and Credit Cards are accepted by most banks or some upscale hotels and restaurants and shops, but only in Phnom Penh, Siem Reap, Sihanoukville and the casinos in Poipet, you must pay 2 - 4% fee to accept credit cards. The most commonly accepted credit card is Visacard while Mastercard and JCB are growing in popularity. A few places accept AMEX. ATM is mostly not available in Cambodia, so if you plan to travel to outskirts, it is advisable to carry US Dollar bills in small denominations. In case of journey to remote areas it is, of course, advisable to take a good supply of Riel with you.
Do not exchange all of your cash into the local currency at one time, but gradually. It is difficult to exchange back to foreign currency, or with terrible exchange rate - practically impossible for ordinary tourists!
Money changers offer a slightly better rate that the banks. They tend to cluster around the traditional markets. There is usually a section of a traditional market dedicated to moneychangers and gold sellers.
When accepting US dollars, inspect the bills carefully. Marred riel is acceptable tender, but the tiniest tear in a large US note renders it worthless.