Toiletries and Medical Supplies: Make sure you bring some heavy-duty aspirin and also stuff like decongestants etc as altitude sickness can do strange things to you. I would wake up at very odd times with a splitting headache etc so thankfully I had some aspirin handy!
Luggage and bags: In general La Paz is temperate or cool during the day and very cold at night. Unless it is very sunny you will always need at least a long sleves shirt. Bring winter clothes for the evening and cold winter days.
Dress warm! We slept at -25 degrees. But there is nothing better than waking up and taking a hot thermal bath during a gorgeous Andean sunrise.
Camping/Beach/Outdoor Gear: The warmest sleeping bag you have and all the clothes you could wear.
Miscellaneous: A hat with ear protection will go along way. Bring candles and lanterns.
La Paz is cold the year around because of its altitude (3600 m.). But is a dry climate. It's temperature ranges from 4 C to 25 C. When the sun shines you must use sun protection if you stay to long at the sun.
Toiletries and Medical Supplies: The altitude is a problem for some people. Try to have a 'mate de coca' when you arrive or a pill like 'sorojchi pills'.
And if you came by plane from the sea level try to rest the first day.
There are no any mosquitos and insects in La Paz.
Photo Equipment: In La Paz you can find all the batteries and films needed. If you run out of them will be a good place to have new ones. Altough they are sold in the street is better to buy them from a store or film developing center. If you have problems with you camera Mr. Calla at Photo Linares (c. Loayza entre Camacho y Mercado) will help you fixing it (many tourist trust in him).
If you want to have your photos you can develop at AGFA centers. It cost Bs. 6 for the developing and Bs. 1.20 for each picture. They do the work in 2 to 4 hours.
Camping/Beach/Outdoor Gear: If you plan a day out to Los Yungas use inscet repelent. There are many mosquitos around there.
If you go to El Altiplano (Tiwanaku, Chacaltaya, Lago Titicaca) use sun protection and don't use t-shirts. The sun is stronger in the altitude.
Toiletries and Medical Supplies:
Of course, always carry toilet paper as there won't be any except in the nicest of places.
Photo Equipment: Wide angle is always good for building photography.
Miscellaneous: A very special friend for a coffee is always nice....