New York steak???

What would you like to have for your main course?
I think I'll have the New York steak.


I just typed into conversation book that bove sentences.
以上句子我只是在會話書抄回來...
The first sentence why add (to have) into sentence?
第一句點解要加 to have...
If the first sentence (cut to have), the sentence is fullness.
如果第一句沒有 to have, 這句子還是完整嗎?


還有第二句 I'll ..即是 I shall 或 I will, 我好想問一個問題,對於一些初學讀者來說,是否要讀回 shall or will, 還是都是一樣,只讀 I'll 就可以了,,,還有一個問題,看電影,看會話書,他們都有同樣的會話, I remember I ......或 I think I...... 比我的感覺外國人都是想到什麼就講什麼,這樣說好像簡化了複雜的會話,我們可以跟他們這樣說嗎? I remenber I....or I think I.....