Sausage can be as easy as leftovers. No casing. Just meat and spices.
The other night, I had a half-pound of ground pork left after making burgers the day before. I added a half teaspoon of salt, a half teaspoon of French four-spice blend, a pinch of black pepper, and a splash of water. Mixed thoroughly and had tasty uncased sausage meat. You don't have to have casing or a grinder to get started.