It depends on the age and personalities of the people. If you are hanging out around them listen for clues. I had a friend when we went out to dinner she was complaining she didn't have a nice clutch purse, so I got her one. I had a friend whose daughter loved playing with her mothers pots and pans so I got her play ones. Just keep your eyes and ears open.
well I have done this a few times and its great so you get a container loads of notes and you pour a smallish amount of water into the container and put one note in and freeze it and keep doing this until all your notes are frozen buy a cheap hammer from the $2 shop and then give it to the person on their birthday