You don't need to get fancy or spend too much money buying anything for your first time Precision Cooking. Resealable freezer grade plastic bags are a great option, because they are ridiculously easy to find, can take the heat, and are relatively cheap.
You can also explore many other options including silicone reusable bags and vacuum sealed.
Buying food grade vacuum sealing bags is a great option if you don't mind spending a little money. This option does a great job of getting all of the air out of the bag, but it's not necessary unless you prefer it.
If you feel like skipping out on the plastic, another option is resealable and reusable silicone bags. We recommend you do your own research on bags and choose what works best for you and your lifestyle.