How to address students who do not attend, yet want to keep up with the course?

I'll look at these two points:

1) Your course is structured in a way that there is no any alternative way to acquire the materials you cover in class; attending the lecture is the only way. AND

2) You have never expressed, either written in syllabus or spoken to the full class, that it's the student's sole responsibility to coordinate with other students/TAs to catch up with the materials they missed when they were absent.

If either of this is yes, I'd at least help the student once, and then make sure the whole class will know of point 2 as soon as possible.

If there are a lot of them waiting for you, try:

1. Name the chapters/sections in the assigned texts that will cover a majority of what you talked about in class.
2. Have them work in group to come up with a strategy on those "what to do," and meet with them as a group to go over their questions.
3. Group them and give a blanket tutorial. You can also make this a challenging task by asking each of the absentees responsible for sorting and summarizing the texts, or have them work on a problem set together.
4. Invest in either a cheap recorder or screen/voice capturing software to archive your lecture, so that you can prevent other situations like this from happening again.

It's hard to give a "should" or "shouldn't." Analyzing the situation case by case and contrasting with our teaching philosophy along the way should be sufficient to hint what to do.