In special cases, such as when forming a plural of a word that is not normally a noun, some writers add an apostrophe for clarity.
Example: Here are some do's and don'ts.
In that sentence, the verb do is used as a plural noun, and the apostrophe was added because the writer felt that dos was confusing. Not all writers agree; some see no problem with dos and don'ts. (Source.)
So I can imagine that many would say to-do's is ok. to-does doesn't seem right, though I can't explicitly exclude it.
However, according to the Free Dictionary  and Merriam-Webster , the plural form is
The original question asks for the plural of to-do, but OP's given examples might sound funny or odd. Instead, you could say "I have a long to-do list" or "I have many things on my to-do list", for starters.
Speaking of lists, you could also say "I have a laundry list of things to do", though this is an aside :)