You've got a big presentation tomorrow, yet you're totally chill about it.
Literal
Tomorrow, important presentation [subject-が] exist [quotative-って] say [concessive-のに], calm-and-collected [copula-だね].
余裕綽々 (よゆうしゃくしゃく) is a 四字熟語 (four-character idiom) meaning 'calm and composed, with plenty of room to spare.' Combined with って言うのに ('despite saying...'), the speaker marvels at the listener's coolness. って is the casual quotative equivalent of と, frequently contracted further to っ. プレゼン is the short form of プレゼンテーション (presentation).