I'm just an internet commenter who knows nothing about running a retail store and has thought about a bookstore as well. With that out of the way, finding high margin items to sell to offset low margin items would make sense. I think this is why you see coffee paired with bookstores, coffee should be high margin but might also require food licensing/inspections.

Ideas for a local bookstore: seasonal and local items for sale, think gift giving timeframes - mothers day, fathers day, end of year holidays. Items like unique greeting cards, calendars, custom gift wrapping, having a kids section with higher margin items kids like - toys, trading cards, etc. Also you could throw some checkout friendly things like book lights, book marks, candies, etc.

If you find local craftspeople, offer some shelf/floor space for free if you can agree on a split of the margin. Hand-crafted things would pair well during holiday seasons and advertised properly might get repeat visits and word of mouth spreading.