I visited a Bangkok Flood gate and the island formed by the flood relief canal recently. I met a women who sells these delightful flowers made from Bituoy leaves (Bituoy the leaf also known as Pandan has a pleasant candy sweet smell and is used to flavour desserts.)
She suggests you keep them in the fridge to make the fridge smell nice, but I like to have them on my table. She sells them at the market next to Imperial World Samrong Branch, they were 20 Baht (less than $1), see the green arrow on the map below. They last about days before they become too dry and brown.