Don Khon has a better selection of eateries compared to Don Dhet with a generally better quality of food. Prices, however, remain comparable and very affordable. If you're staying on Don Dhet, try and peel yourself out of the hammock for at least one night to sample something of what Don Dhet has to offer.
Pan's Place offers food that is better than much of what is offer on Don Dhet, serving up a good mix of Western and Lao food with a couple of Thai dishes thrown in the mix.
The restaurant at Sala Done Khone is a top one but priced accordingly -- go there for something a little bit more special.
Down by the Khone Po Soi Waterfall is a nifty little spot for relaxing with a beer and perhaps chowing down a tasty Lao dish. The restaurant is perched on the edge of the river which makes up the waterfall and the sound of the waterfall combined with the quite remote feeling of the place comes together to provide visitors with a great spot to have a meal. It's worth the bicycle ride out here for lunch if you're staying on the island for a couple of days, but not an option at night.