The tour is just over night: You can go minimal and carry a pair of shorts for Sunday & a credit card. A windbreaker for the evening & if your SPD shoes won't work, carry a pair of sandals... Keep toiletries to a minimum... With the credit card you can buy food, drinks, & a fresh t-shirt in Carlsbad to wear in the evening & home Sunday!

Even a good sized handlebar bag could carry this minimal! I would not want to wear a day pack - but it has been done; and if you already use a camel back you could slip the minimal gear into it's pockets!

If you have a bike with eyelets on the frame, you can attach a rear rack & carry plenty and more in a small trunk bag or duffel. If not, or want to snap a rack on your road bike's seat post, there are clamp on racks available; Many shops and stores have gear; REI is just one but they also have a full line of compact light weight gear for cyclotouring/backpacking/paddling...

Camping? Add a sweater, light sleeping bag, tent & insulite pad or therma-rest & you are set... Panniers carry way more than you will need overnight, unless you want to cook food in camp... A 36" duffel with a sheet of cardboard to keep it out of the spokes will work fine as a saddle bag...

 Low Budget pannier / saddle bag set up for light camping:

Get a touring rack; a back-packing sleeping pad & light tent; & a 36" duffel bag with full zipper (or better yet - double ended zipper)

Cut out a sheet of cardboard to line inside bottom & both ends of duffel bag:

(Fold over rack & up on each end; keeps duffel flat near wheels & keeps ends from bulging into street)

Put sleeping bag across bottom of duffel, & stuff extra clothes, shoes etc at both ends. Keep middle flat to drape over the rack...

Drape duffel over rack & strap on or wrap with bungee cords. Make sure the front of the duffel clears your heels when you pedal. Hold tent & pad on top with more straps or bungee cords.... If it looks like rain, pack along some trash bags to protect the sleeping bed & clothes from water & you're good to go!

If you are able to go with a stuffed sleeping bag, rolled up Therma-rest pad & small tent, I usually stack the stuff bags & strap 'em down parallel to the frame with a few tight elastic 'bungee cords'. This keeps it aerodynamic and easier to mount. If you have a bulkier sleeping bag, tent & 'insolite' pad, you usually have to go perpendicular and the bags will lay across the tops of the panniers.

A down bag will compress very small; find a square summer weight bag; unless you really get cold easily; the extra bulk of a full hood mummy bag is not worth packing.Therma-rest bags are foam padded air mattresses; Compress well, comfy & none of the bounce of an air mattress. Insulite is a dense closed cell foam pad back packers use. Lighter, cheeper, and won't leak - but a bit more bulk to pack. Small back pack tents are light & compress easily. Unless doing some serious touring I would not worry about 3 or 4 season tents; if the weather is that bad I'm pulling out a credit card for lodging. Make sure that the poles breakdown into short lengths and many will stand with out pegs in the ground unless a strong wind comes up. Rain flies are better for rain & left off when dry - the moisture from your breathing will condense inside a water proof tent & drip on you in the morning. It takes time to dry it off before you pack & roll out as well. For the Solstice it will be a bit misty in the morning but you can probably leave the rain fly at home.

Unless you really get into touring and/or back packing - I'd RENT!

Strapped down stuff bags with bungee cords