make sure that everything is ready这个宾语从句的that能省吗

可以省略,但是请注意不能省略的情况如下:
宾语从句中that一般情况可省 ,但也并不是任何情况下都可以省略.
具体如下：
He told us that he felt ill.他对我们说他感到不舒服.
I know he has returned.我知道他已经回来了.(that省略)
注:宾语从句中that一般情况可省 ,但that在引导宾语从句时也并不是任何情况下都可以省略.在以下情况下,that不能省略.
1． Everybody could see what happened and that Tom was frightened.(and连接两个宾语从句,that宾语从句放在and的后面时,that不能省略.)
2．I know nothing about him except that he is from the south.(that引导的宾语从句作介词宾语时,that不能省略.)
3．That he ever said such a thing I simply don’t believe.(that从句位于句首时,that不可省略.)
4． We decided,in view of his special circumstances,that we would admit him for a probationary period.(主句谓语动词与that从句之间有插入语,that不可省略.)

可以

可以

可以的。
宾语从句的引导词that可以省略。