To perform a spell, it is not necessary to cast a circle every time. The circle is a sacred space of protection and I would recommend getting into the practice of doing it, but it is entirely up to you. It simply depends on what you feel comfortable with.
Not all spells require items, either. There are many different types of spells. Some only require an incantation, others are even more minimalistic than that. You can also create your own spells with whatever you have available to you, as long as you understand their powers/abilities.