Now is the time to get that digital recorder, tape recorder, notebook and pen and pencils.
Family is going to get together, those special times you are spending with your own family ~write it down~
Take photos – but put names on photos. Copy on copy paper, those photos you have and take with you, so your relatives can identify them for you and that way you keep the originals at home.
Same for letters you might have or other documents, take copies of them to take with you and share and then record or write down the stories and identifications and history that goes along with them.
Where were they taken, written from/to, who do they pertain to, what is the circumstance for the photo or letter or document, which family do they belong to. What else do you know about the situation regarding the photo, letters or documents?
Have fun, makes some calls ahead of time with people you are going to see. Keep those connections open before you see them, you may be surprised at what you can find out about your own family.