Well, yes and no. While I can never be 100% certain that I exist (no not cogito ergo sum, cogito ergo sum is silly) it's a pretty good bet that I do and if I don't then so what? What could I possibly do? If I don't exist then what is this? I dunno, but it's fun so I'll keep doing it.
Anyway, no I don't anything for certain, I'm possibly even unsure of the certainty that things are uncertain. But I do know that this is my lot and I shall deal with it. Killing myself seems a little premature since data suggests we die anyway and I may as well suppose this life is finite since there's nothing to suggest otherwise. Railing at the possibility of being non existent seems a little bizarre and more importantly pointless.
If we take my existence for granted then there are lots of things I'm sure about. I know, without doubt, that I am an agnostic atheist, that I have several qualifications, that I have in depth knowledge of social interactions and human behaviour, that I like the taste and texture of most breads. I know that I like plants and I like rocks. I love to climb things and I enjoy running and exercising. I like to argue and debate and like to win but have come to accept that losing is OK too and that gaining insight is more important than being right. I know that I love sex and I only seem to enjoy (in prospect at least) sexual intimacy with women. I know that sometimes I get tired when I shouldn't be and sometimes I'm singing and dancing at 4am and will be fine despite not sleeping. I know that mead is my favourite drink and that I dislike the taste of cigarettes but don't mind the smell so much.
If we take my existence as sure, many things are certain. I don't know if I exist, but I enjoy whatever this is and there seems to be little point in railing against it. I also seem to have some impact on the lives of others which is generally considered beneficial. So for now at least I'm more than content to live...or not as the case may be.
eta:
Since it's been said a few times I'll refute cogito ergo sum (I think therefore I am):
Descartes tried to remove all preconceptions in case of deception before beginning his thoughts (meditations). Cogito ergo sum was his first conclusion, that thoughts required a thinker. However if we're removing all preconceptions, then thoughts do not require a thinker, that is something we have observed and is no more reliable than I exist because I've seen myself in the mirror or I exist because I exist. It makes no sense.
Furthermore the cogito is essentially debatable, thinking may require a thinker but there's always the question of what thinking is, what if you're a machine, processing the work of another being, OK in this scenario you exist but not by virtue of thought, you simply exist. Thoughts are not necessary in existing things, nor is it necessary (again, no preconceptions) for thinkers where thoughts are.
Descartes failed to remove himself entirely, his meditations were heavily criticised at the time and continue to be regarded as of interest but wrong. Unfortunately the nature of people is pretty soundbites work, it may be wrong but it's become popular philosophy and many think it's true.