There are many things you can use when you don’t have a yoga mat. A towel, as thick or thin as you prefer, will be enough to give you that yoga mat feeling during practice. Some people even opt for a bath mat if they find one big enough! Any kind of blankets or old woven mats will also suffice. If you really have nothing, just find a spot on a grassy patch that is flat and soft. And make it a short practice filled with poses that are not too dangerous or really challenge your balance.