Plants do really help to keep the water clean and healthy for your fish. I currently have a 2 gallon drum bowl that is pictured below.
As you can see, a soil base is perfectly feasible in a 2 gallon tank, and will definitely help your plants grow better. However, it is very important that if you decide to go with a soil based tank that you get rooting plants instead of just stem plants. Also, with a planted tank, never do a 100% change, especially with a soil based planted tank! However, gravel is perfectly fine to keep using as well. This tank started out as a gravel base and I added the soil later, but it still has a gravel cap.
Some good plants to start with if you aren't doing a soil base are anubias, java fern, marimo moss balls, and anacharis. These all have low light requirements. It is essential that you have proper lighting, especially if you want to have a greater variety of plants than listed above. A 6500K temp bulb in a basic desk lamp over the tank will work fine. The importance is the color temp of the bulb. The actual wattage won't matter much here, but will probably be around 10-15 watts for a compact fluorescent. Buy as many plants as you can afford, but make sure you have the right lighting!
For this tank I use this heater: http://www.amazon.com/Elite-Submersi.../dp/B00106X8QG
Fully submersible and adjustable even though it says "preset". Also, it isn't too expensive really, especially if you need to order other things and can swing super saver shipping. :)
As far as food, New Life Spectrum is considered by many to be the best. I personally like the small fish formula, or the ones infused with garlic, but even the ones made especially for bettas are fine. You can also feed frozen bloodworms or brine shrimp, but I understand if you aren't comfortable with that.