@JackieWeaver It's polite not to pick stuff without checking - for example if someones's trying to hybridise or duplicate flowers, then picking will interfere with that. I've got lots of fruit trees I don't mind being shaken but there are a couple I don't want touched.
People on this thread tend to leave out DIYs and items for visitors but if it's your first visit it would be polite to check before taking. Sometimes items are left out for cataloguing, not taking, so it's worth being sure.
I wouldn't pick up shells or star fragments from someone else's beach. If I spotted Gulliver or a DIY bottle I'd let the host know.
There are some amazing islands on this thread - it's well worth visiting to get ideas. People here are so helpful and friendly - if you need any items or help with anything just ask!