A piece of advice: Begin packing several weeks in advance to avoid last-minute shopping or at least check this list.

Workout gear
10 T-Shirts and 6/10 gym shorts
10 pairs of socks
2 pairs of basketball shoes (It is not a good idea new shoes)
2 sweatshirts and tracksuit

Daily Clothes: casual clothing
Shorts, pants, T-Shirts
Fleece jacket or sweaters and thin raincoat
Plenty of socks and underwear
Pijamas/nightdress
Beach towel, 2 bathing suits, bathing cap (compulsory for the swimming pool), hat for the sun
Shoes or sandals and flip-flops for the shower and the swimming pool
Sunglasses
Small toiletries kit or basket so your child can carry and keep track of essentials such as soap, shampoo, toothpaste, toothbrush, floss, deodorant, comb and brush. Bath Robe .
Sunscreen
Fun
Towels for the shower
. * Electricity supply in Spain is AC 220 Volts, 50 Hertz. Sockets meet European regulations and use the round pin system. Bring adaptors and make sure that the electrical appliances you are going to use (computer, mobile phone charger, shavers, fun…) work at this voltage.
* Put your child's name or initials on everything —clothes, hat, swim suit, towels— with either a laundry marker or iron- or sew-on labels.
* Laundry bag for wet or dirty clothing with your child's name

Documents, medicines
— Passport (Original and three copies)
— 2 photos
— Medication if needed. Send medication in its original container, along with explicit dosage instructions to the camp nurse or healthcare facility. A signed medical-release form should accompany all prescription medication (in English or Spanish).
— Parental Permission form.
— Medical Certificate and Release and Waiver
* If camper has glasses or contact lents, bring 2 glasses and contact lens cleaner.

For the Spanish lessons
Pocket dictionnary.
Some material for the lessons (notebook, pens…)

Other items
BackPack or something similar to go to the Camp, for off-campus activities and excursions.
Camera and batteries
Cell phone (and charger) /calling card

Could be a good idea to download and print the items to bring tho the Basketball Camp and check them because probably we forgot something that your child consider important.