5 gallon tank Great!!
aqua clear 20 (filter) good, just be careful with it as it can be really strong in 5 gallon. Here are links to some baffles you can use:
http://www.bettafish.com/showthread.php?t=30139 and
http://www.bettafish.com/showthread.php?t=56100 Also you can put some pantyhose or foam over the intake so it doesn't suck your boy in either.
Elite 6-Inch Mini Thermostatic (Heater), 25-Watt That heater is fine but I suggest this one:
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3743+11368&pcatid=11368 it's submersible which will make your life a little easier when placing it in the tank and with Betta tanks I always find that my water line is not to the top to prevent them from jumping out because they will, so it makes it easier to place the heater.
Seachem Prime (Conditioner) Great! I also suggest getting some Stress Coat water conditioner. It's a conditioner with aloe in it which will help heal your Betta's fins when they get ripped, it's practically inevitable so mind as well get it now ;-)
New Life Spectrum Small Fish Formula (food) Love it! The Betta formula is good to if you find it, it's basically the same formula, I just like the container pictures better XD haha
Fish net (I have an old one that I will sterilize) Don't use a net, it will rip and tear their fins. Instead use a small plastic cup, I use the ones that my Betta's came in from PetCo/PetSmart/PetSense and I just scoop them out with some of their water and voila, fish in a cup lol
Freeze dried blood worms Don't get these if you don't have to. They promote constipation which obviously is no good, you can use them as a treat maybe once a week but I really wouldn't use them if you don't have to. If you can, get Frozen BW instead, much healthier and easier for your little one to digest.
Silk or fabric plant. I don't know which one to get.
Silk and Fabric plants are pretty much interchangable as long as you don't get anything with plastic on it, you'll be fine.
Zoomed leaf hammock (and if enough room in tank, The log) They should both fit ^_^
Ph and Ammonia test strips Instead of getting just the pH and ammonia test strips get the API Liquid Master Testing Kit, yeah it's a bit more expensive. Don't get it in the store if you can help it, I've found it on Ebay for 14-16 dollars at one point. The reason is that the strips are extremely inaccurate because of how they are stored no matter what you do. So you can get a reliable testing kit with more. To know if you tank is cycled you need Ammonia, Nitrite and Nitrate
at least and then the pH and the other two are just nice to have although pH is pretty important as well. But it will just save you money down the road even if there's shipping, it's worth it.
I also have aquarium salt ready to use if nessasary. That's good! And just a forewarning, sorry if you already know but it always bares repeating! --Don't use AQ salt on a weekly basis with Betta's as the salt actually creates liver/kidney failure which can lead to dropsy which is no good! But it can be used for 14 days with no ill side effects usually and if you need more than 14 days, depending on the dosage you can give a break of 4-6 days and start again.
I will cycle the tank with fish food; I heard you can put the food in a nylon sock to keep the tank clean. With fish food? Not in the nylon, what you'd be talking about is a raw shrimp in the nylon. With fish food you just grind it up and throw it in every other day and let it rot while keeping an eye on your ammonia and nitrites.
Thermometer (which one should I get?) Not the stick on ones, get the glass one at Wal-Mart for a dollar something. Funny because the glass one is actually cheaper than the stick on ones XD At least at Wal-Mart it is haha but any glass ones will do as they are more accurate and easy to see :-D
