I found this small presentation pack in a gift shop. I recognised the stamp, but I had not seen the coin before. Both items commemorate the Royal Barge Suphannahong taking part in the Royal Barge Procession in Thailand.
This stamp was issued on 13th November 1997, commemorating the Royal Barge Procession in general, and in particular (I think) the first launch of the Royal Barge Suphannahong on the same day in 1911. Royal barges have been a tradition in Thailand for several centuries.
In the background, you can see Wat Arun – the Temple of Dawn – on the Chao Phraya River (“River of Kings”) in Bangkok. Wat Arun is the destination of the procession, which is held on auspicious occasions.
The coin is a commemorative 1 baht coin (0.03 USD), issued in 1977. It features the distinctive “swan neck” of the the Royal Barge Suphannahong.