Minimal reference content

What information is mandatory depends on the applied reference style, e.g. APA6 oder Chicago Style. The reference style even sets the number of authors listed maximum in the reference. Most of the times, the journal/conference sets the reference style you have to apply.

Usually, the mandatory information for journal/conference papers includes:

• Author(s) name(s)
• Title
• Year
• Journal/Conference name
• Page number
• DOI

The only real option to shorten anything is to use the abbreviations of journals/conferences. But the applied reference style might even prevent this trick.

Does the venue impose a particular bibliography format? If not: I'd consider DOIs useful but not obligatory, and I've never seen a plain bibliography with abstracts and keywords (that would be an annotated bibliography).

Many journals/conferences impose style requirements on in-text citations and reference lists. If left to your own style, the standard goal is for the in-text citations to uniquely refer to a single item in the reference list. You might be able to save a couple of characters if the in-text citation refers to a group of items, but don't do this. Numeric in-text citations tend to take up less space than author-year and label based styles.

For the reference list, the goal is for each reference to refer uniquely to a single published item. The DOI alone would accomplish this, but might be more characters than the journal, volume, and page number. The authors, title and year, are almost always redundant and require more characters than the journal, volume and page number. It is important to realize that most people want a little more than the minimum and like to see the author and title.