Congratulations on acquiring your beer-brewing kit. For whatever it's worth, I didn't find the thermometer that came with my kit to be especially useful. It's a glass alcohol thermometer, and quite fragile, and I didn't really want to use it around my wort. I've put it in my darkroom, where an extra thermometer for measuring solution temperatures comes in very handy. I just used my digital meat probe (sanitized, of course), to measure my wort temp before pitching the yeast.
I like my hydrometer. Yes, it's true you don't really need one, but I recorded my OG, and I'll take another reading in a day or so. I just like the idea of tracking the gravity of my beer so that, over time, I'll come to understand how it relates to the progress of fermentation and the final alcohol content, and so forth. Also because I'm an inveterate note-taker anyway.