How to use infinitive after 'to be' verbs?

I wonder how an infinitive should be used after a to be verbs, i.e. does the infinitive used this way have to use 'to' or not. For example:

1. All you have to do is sit (or to sit or sitting??) and wait.


2. So, what we did in this lecture was create (to create or creating??) a new style for our activity ...

Answer

1. 
   

   All you have to do is (to) sit and wait.

   
   
   


2. 
   

   So, what we did in this lecture was (to) create a new style for our activity ...

   
   

It must be an infinitival verb phrase. Gerund-participial clauses (the -ing kind) are not permitted here.

The bare infinitival (without the to) is usual, but where the subject noun phrase contains do in a relative clause, as it does in both your examples, to can be optionally added.