Take a walk amongst the flowers at Utrecht's Bloemenmarkt
Saturdays in Utrecht, stroll through rows and rows of potted plants and brightly colored blooms in Janskerkhof plaza, and then make your way to Oude Gracht (the old canal) and shop for a bouquet to brighten up your apartment or hotel room. Big bunches of roses and tulips seem ridiculously cheap when compared to the cost of buying flowers elsewhere-- 5 euros will easily get you something gorgeous and fresh.
Note: Depending on where you fly home to, purchasing and importing live plants or seeds may be illegal. Check it out ahead of time to avoid the heart-break and hassle when you're forced to leave your living souvenir behind, and pay a fee besides.