Die-cut vinyl stickers are fun and waterproof. They tend to be long lasting, and can weather a lot of wear and tear when used on items you use every day. I personally have one on my cellphone case and another on my waterbottle. I carry my cellphone in my pocket.
Stickers can ship multiple at a time. They are fulfilled as print to order, meaning that production time must be accounted for. Most stickers ship within 1-2 weeks.