What are some examples of "service activities" for the inexperienced/up-and-coming academic?
As for the question in the title, some common examples would be organising a seminar, helping to organise a conference or workshop, or serving on a committee.

I don't think that the activities you mention are generally considered 'service'.  They are definitely activities worth mentioning in other contexts, though.

If you really don't have any experience in 'service activities', then perhaps a good way to respond to questions about service would be to admit that you don't have such experience so far, but express interest in gaining such experience (with specific details of the kinds of service you are especially interested in).  I have no idea whether this is good advice, though, as I'm only a postdoc myself and have never been on a search committee.