How to deal with co-authors' tardiness? I have a paper due tonight, and I have done my part. I have also volunteered to compile the texts from the other authors and hand it all in (there's four of us). I have all texts except one and frankly don't expect to get it on time (our internal deadline was two days ago.)

How should I handle this situation? Leave the whole section empty, with an explanatory editor's note? Just take it out? Send an explanatory email to my lecturer?
The correct answer is not to wait until two days before the deadline to check in on your co-author's progress. Presumably this is no longer an option.

If the section is not necessary, take it out. If it is necessary, you and your non-tardy co-authors can try to get together and do it together before the final deadline. 

You should certainly tell the tardy co-author what you plan to do (I mean the collective "you," as in you and your other co-authors). 

If the tardy co-author's contribution doesn't make it in before the final deadline, then his name won't go on it either.

Note that if this was a paper being submitted for publication, e.g. a conference submission, and not for school, you would likely just miss this deadline entirely and have to wait to submit to another conference.