I'm not sure what that means. Does he mean Sanders has too much baggage? Because that is different from having things "in the bag," which is not necessarily a negative. Having something "in the bag" means you have it cinched up, or as good as done, doesn't it?
In the context of the entire conversation, he clearly meant "too much baggage" or something equivalent.
The first thing that happens is that he's asked about Bernie, and says they have "two things" in common. Not a whole bunch of things -- Trump just says "two". He says the two things are 1) that they both draw big crowds, and 2) that they both think the country got screwed on trade deals. But he then says that Bernie has absolutely no idea how to negotiate good trade deals. So Trump immediate undercut the only area of policy agreement he identified.
The questioner keeps pushing though, and is then obviously trying to get him to sign on to the Bernie. He responds to Trump's point that Bernie doesn't have a clue by saying "But he could learn from you as your number two, right?" So the questioner is trying to overcome Trump's objection, and that's when Trump responds by saying that Bernie has "too many things in the bag". It's an odd phrasing for
"too much baggage", and perhaps it's a New York or New Jersey thing, but the meaning in context seems pretty clear -- he's rejecting the idea that the possibility that Bernie could learn how to negotiate trade deals on the job could make him an acceptable VP, which is consistent with him identifying previously only two commonalities.
I don't like Trump -- I think that he's unworthy of being considered for support unless he apologizes for his conduct towards other candidates in the primary, and he's not going to do that. I just don't think it does us any good to try to manufacture specific controversies when there are so many far more clear areas where he's deserving of condemnation.
Also, the reality is this -- the President does not have the authority to select the VP. The Convention itself must approve the VP the same as it must approve the President, and there's no way the GOP would ever accept Sanders as VP. So this article is someone trying to manufacture a controversy where none really exists.