According to Fedex: Cambodia Country Profile it is illegal to import "Perishable foodstuffs and foods and beverages requiring refrigeration or other environmental control."
You are able to bring an unopened jar of Vegemite into Cambodia; however, if it is opened, according to the Vegemite label, it must be refrigerated and consumed within four weeks. Unfortunately this means that any opened jar is destined for the garbage can at Cambodian customs.
Promite is another vegetable extract product similar to Vegemite that, according to the label, does not require refrigeration, therefore it is possible to bring it into Cambodia opened.
Air travelers are prohibited from carrying on more than 100 milliliters or 100 grams of a gel, therefore any container larger than this would have to be checked in.
