My 15 yo is apparently too cool for DIY kits and doesn't like acessories or makeup I get her, so it's mostly gift cards to stores where she can get things she likes. Last year there was a Steam gift card and this year I got her Clipify subscription since she's interested in video editing and has started her own vlog.
Things like power banks, ring lights, headphones are hits.
There are plenty of subscription boxes your 16 yo may find interesting www.mysubscriptionaddiction.com/best-subscription-boxes-for-teens