Do I need a vacuum sealer?
While it is ideal to use a vacuum sealer with sous vide cooking, it is not required, or your only option.
If you don’t have a vacuum sealer, you can use the barometric pressure from the water to give your food a great vacuum-like seal. This method is called the 'Water Displacement Method', and we here at Nomiku use this method regularly.
A video tutorial of how to use the 'Water Displacement Method' with your Nomiku can be viewed here.
Also, this topic is discussed in this Cooking Issues post.