。
I have a lot to do today.
Literal
I [topic-は] today [contrast-は] do [nominalizer-こと] [subject-が] many exist.
することがたくさんある ('there are many things to do') — する nominalized with こと. Double は: 僕は (topic) and 今日は (contrastive/temporal). たくさん ('many, a lot').