Prados del Sol
Preparing for the rain and for the sun, I have a lot of experience and I strongly recommend 2 companies for their hats and rain/sun slickers.
Choosing between an oilskin hat, a Tilley hat, and a cheap knockoff of the Tilley.
As far as slickers go. I have an Outback Stockman oilskin duster. The stockman is longer, providing more rain protection for your legs. It and the shorter Low Rider duster are designed to work perfectly when riding a horse or out walking in your field, so they are in my mind perfect for walking in Costa Rica sun or rain. They are fairly light and won't provide a lot of extra warmth in cold weather: in Canada where it gets down to -40C in my area, I wear a sweater or a 2nd shirt and sweater depending on how cold it is, but in Costa Rica, I just wear a light shirt under it. In the heat and sun, it can be too much though - so I wear it for short trips in the sun as very convenient sunscreen or when it is raining, but not for long walks in the sun - it is too hot.
Where to buy:
As far as camera's and cell phones, I've done everything from a plastic bag to a waterproof hard case for a camera I owned many years ago that I made myself out of plexiglass and silicon sealant for the waterproof part. It was good down to 3' below water - I didn't try it lower than that. So I don't have any real suggestions on this even though I've used a lot of water proofing/water protecting equipment through the years. The costs vary greatly and what they do and how inconvenient they are varies.
Currently for cameras, I use a plastic bag for my Nikon and Canon equipment, a plastic sheet for my 4x5 view camera, and a waterproof bag I got online for $3 for my cell phone. All work for me!
I also don't have any suggestions for boots. I wear Red Head heavily insulated high boots for -65C to +50C (I like the insulation at both extremes!) but I have duck feet - 9EEEE in the front, 9 in the back) so I have very limited options for good footwear, most footwear that claims to be 'wide' is not wide enough for me. I also wear crocs, but they wear out quickly walking on gravel, so I use them on sand, grass and airplane if I don't have my hikers with me. I wear the hikers on the plane then because they would take up way too much room in my carry on or luggage-and I like to take a lot of stuff ranging from computers to cameras with me when I travel, so wearing all the bulky stuff on the plane lets me take more of my "stuff."