As was mentioned earlier,.. climbing partners are ABSOLUTELY
about Trust! Whether top roping or lead climbing, you literally have each others lives in your hands. NEVER
climb with, or trust your safety to the equipment, if it's someone you don't know or trust completely!!!
No one has mentioned this yet, but as for "used" equipment,... Helmets maybe, rope bags & accessory cords /webbing, sure!! But as for ropes, anchor webbing and harnesses, buy new!!!!
your ropes history, age, maintenance, how many & what types of falls it has arrested! I probably wouldn't trust used biners or nuts either!!!
Also, learn your knots! I have several two & three foot lengths of 9 & 12mm cord and various pieces of webbing that I carried around so that I could practice tying my knots just about anywhere.
Also, you might want to check out these books (pamphlets almost!) They are really old, but they have really good information and lots of illustrations showing how to properly tie all types of knots for climbing.
"Basic Rockcraft" by Royal Robbins La Siesta Press
Basic Rockcraft by Royal Robbins: La Siesta Pr 9780910856348 Paperback - OwlsBooks
"Ropes, Knots and Slings for Climbers" Walt Wheelock La Siesta Press
ROPES KNOTS AND SLINGS FOR CLIMBERS BY WALT WHEELOCK LA SIESTA PRESS on eBay!
They look, and ARE really dated, but the basic info's good!
Hope You & the (GF/Fiancée,..) Have a blast!!!