Actually, my oldest friend sent me a really lovely parcel of stuff of that theme. It had a gorgeous letter in it about how proud she is of me (which made me cry!) & about how she didn't think that I'd need help with the 'proper' bits & pieces, but she'd send:
a enlarged copy of a ridiculous entry I wrote in her blue diary in 2001 (something old), a really cute blue babygro (something new), & a blue bottle of her favourite perfume which I'll wear tomorrow (something borrowed).
More traditionally, I have a blue garter, my dress, & an old family brooch which was my great-grandmother's & has been worn by every woman in the family at her wedding since (it's a bit ugly, but I'll pull it off ).