Mountain Biking - Mountain Bike Accessories?

So I just sold some things and got a little extra money and I want to use some of the money to upgrade my dads new mountain bike. He built it himself, starting with a really nice lightspeed frame. He's really into carbon fiber stuff, and he wants to make his bike light. He isn't a "mountain biker" per say, he just rides it from fishing hole to fishing hole, but he's been really good to me over the years and I'd like to do something nice for him. He's 65 so he's not a young guy by any means.

I have around $300 to spend, but that doesn't mean i need to spend all of it.

I thought about maybe a set of disk breaks, or a carbon fiber fork/seat post/handlebars.

So, forum, any suggestions? And if you could lead me to good websites that'd be awesome too.

Thanks!!

Any idea what he has on there now? That might help us with where to start. I know that's a tough one since it's not your bike, but it's hard to make suggestions when we don't know what he already has. Also, what kind of terrain is this? Are we talking about paved roads? Fire roads? Something a little more technical?

Seat post and handlebars are nice options that would fit into your price range. How about a rack or panniers to haul his fishing eqt. How are his rims. Reducing Rotating weight is a big effort saver.

Where does he fish. At one point I believed that finding remote fishing ponds was the primary reason MTBs were invented.

Search Jensons, pricepoint, chainreaction, huckandroll. Doing an ebay or Amazon search might get bogged down with trash in the quality stuff.

If he built the thing up himself from scratch I'd bet he already has a decent seat post and handlebar. You might want to check and see if he has fenders and / or a lighting system. Both of those are available in models that are easy on / easy off so he can decide when it's practical to use them without having to drive with them installed all the time. For example Topeak make a couple different models of fenders like that in the Defender series.

Most of his parts so far, less the frame, are not all that nice. His fork is just one from a trek 4300, and he took the seapost and handlabars off the 4300 as well. He already has the whole pannier setup and everything.