How do you decorate coastal with country or rustic?

https://www.pinterest.com/lynzy/home-farmhouse-meets-coastal-cottage-inspiration/?lp=true

Modern or Contemporary coastal.

https://freshome.com/defining-style-series-modern-coastal-design/

Reclaimed wood always works for rustic. Check out the shelf I made with old fence wood.

Do you mean you now have coastal and want to add country or rustic? Or that you want to just have country or rustic? Driftwood is both coastal and rustic, white ironstone pieces or blue metal mugs, plates etc could be both coastal and country, blue and or green checks could be all three, pillows covered with blue and white pillow ticking could be all three. Small hooked or braided rugs could be all three. When I read your question, the movie "letter in a bottle" popped into my mind. I loved the seaside cottage featured in that movie.

Use distressed white, blue, yellow or green wooden pieces in the shapes of nautical wheels, sailboats, anchors...