。
I'm going shopping tomorrow.
Literal
Tomorrow [topic-は] shopping [purpose-に] go.
Functionally an alternate phrasing of 'I'm going shopping tomorrow,' with は on 明日 setting tomorrow as the topic. The は frames it as 'as for tomorrow, I'll do shopping' — adds a slight 'as for...' nuance compared with a bare 明日 + verb, but doesn't change the meaning.