So peat, pine bark? How far down should I mix? 6 inches, a foot?

Ideally, compost. And a lot of it!! And it will be something that you will need to add repeatedly, as FL heat and moisture will break it down rapidly.

If you want to use the soil for a veggie garden right away, work in a generous layer of well rotted compost/manure (since I don't garden in Florida, I don't know the exact amount that is right for your area; if you wanted to grow okra in my neck of the woods, you'd add 8 inches to the surface before you tilled). Peat moss has a short life span in hot, humid regions, so it's not worth the expense. Wood cellulose, i.e. tree bark, below the surface temporarily ties up soil nitrogen, so incorporate it only if you plan on waiting a year for it to break down. If you're lucky, you could find a stable or dairy farm that has let its manure decompose. Well rotted is the key term. Do not use fresh manure. Any manure you add should no longer be recognizable as manure to your eyes and nose. Otherwise, your best bet is to locate a reputable dealer and buy ready-to-use compost in bulk, usually by the cubic yard.

If you plan on pursuing vegetable gardening a long-term basis, you'll want to make your own compost so you can replenish the organic matter a long growing season tends to deplete.

it is tough. I lived on similar sand, and one foot of wood chips would generate two inches of black soil on top after a few years. One foot! and two inches down it was still beige sand. so compost on top is relatively inefficient in pure sand. for sure plants are water stressed in the situation you describe, as the soil dries in minutes after a rain. Sweet potatoes do better because they are both deep rooted and drought resistant.

so, while you increase OM, you also need to improve water retention. In my experience burying logs (hugelkultur, read about it, you can use the surrounding pines) is the best technique for precisely that. It is best to bury a variety of wood pieces in various states of decomposition,and you don't need to make mounds as in classic HK. The logs will absorb water and the veggie roots will get into them. Eventually you will have loamy patches deep in the soil which will act as water reservoirs. It will take a year or two for the soil to become more retentive. The other thing you need to do for better growing success is grow more deep rooted and/or drought resistant veggies. Okra and cowpeas for summer growing, chicory, beet and carrots for winter.

You need to add enough organic material (that is the raw stuff) to make about 6 to 8 percent organic matter (what is left after the Soil Food Web works on the organic material). That could be compost (predigested organic material) , wood chips, shredded leaves, or any other once living plant material including your food scraps.

The only way to know what the soil pH is would be to have it tested and your University of Florida does a soil test for $7.00. http://soilslab.ifas.ufl.edu/ESTL%20Tests.asp

In addition these simple soil tests may be of some use.

1.Testing for organic
matter. Put about 1 cup soil (enough to fill the jar to 4 inches) in
a clear 1-quart jar, with a tight fitting lid. Fill that jar with water and
replace the lid, tightly. Shake the jar vigorously and then let it stand for 24
hours. Your soil will settle out according to soil particle size and weight.
For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the
bottom. about 1 1) Soil test for organic material. From that soil sample put
enough of the rest to make a 4 inch level
inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about
1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1-foot square and 1 foot deep and fill that
with water. After that water drains away refill the hole with more water and
time how long it takes that to drain away. Anything less than 2 hours and your
soil drains’ too quickly and needs more organic matter to slow that drainage
down. Anything over 6 hours and the soil drains too slowly and needs lots of
organic matter to speed it up.

3) Tilth. Take a handful
of your slightly damp soil and squeeze it tightly. When the pressure is
released the soil should hold together in that clump, but when poked with a
finger that clump should fall apart.

4) Smell. What does your
soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant
odor? The more organic matter in your soil the more active the soil bacteria
will be and the nicer your soil will smell, to a point. Too much organic matter
can be bad as well.

5) Life. How many
earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5,
according to the Natural Resources Conservation Service, indicates a soil that
is not healthy.

All good advice. Also, for more reading, use the search box at the top of the page and search for 'Florida' in this forum. This ain't our first Florida sand rodeo! :-D