A lot of the disdain for supplements is a reaction against those people, usually young people, who buy into the supplement company marketing and think that supplements are the key to health and fitness. They'll eat crappy diets and have crappy training and focus on getting the latest, greatest pills and powders into their mouths. This is silly - you can't supplement your way out of a crappy diet, unless the "supplements" are anabolic steroids, and even then you won't come close to maximizing your potential. That doesn't mean supplements are of no benefit. Think of them like extra stretching sessions - if your training is good, extra stretching will somewhat improve your karate. But stretching alone or instead of real training won't come close to making you a great martial artist.
Down to brass tacks. You do NOT NEED any supplements to be healthy and perform well IF you eat a good diet. By "good diet" I mean lots of grass fed beef (including the organs) and wild caught fish, fresh fruits, vegetables, and berries in a wide variety, and plenty of sunshine year round. So why take supplements?
There are two general reasons. First, some supplements can enhance your performance above what it would be on an excellent diet. A person eating a great diet who added in some creatine would probably see a boost in endurance and size - even a fantastically healthy diet won't supply an optimal dose of creatine. Another example is caffeine. Take a fantastically healthy person in great shape and have them spar for an hour. Compare them to another equally healthy and in-shape person who spars for an hour after taking 250 mg of caffeine. We can argue about the overall benefits of caffeine, but in the short term at least you'll get a definite performance boost out of it.
The second reason to take supplements is to make up for some deficiency in diet or lifestyle. For example, I work indoors in a climate where there isn't much opportunity for sun exposure during half the year. So I take Vitamin D3, 5,000 - 10,000 IU of it, every day. Would it be better to spend hours in the sun with my shirt off? Well, it would be healthier for me, but it's just not going to happen. The same goes for sleep. I'm sure I'd be better off reducing my stress levels, going to bed earlier, and staying away from electronics for an hour and a half before bedtime - but none of that is going to happen. So I take supplementary magnesium before bed, which seems to help my sleep quality.
If you have limited money:
- Seriously consider spending it on better food first. You're going to get a lot more out of a pound of raw butter from grassfed cows than from $10 worth of pills. Upgrading your beef to grassfed and adding in some more fruits and vegetables, are both better investments than anything from a bottle.
- Go with the sure things first. Probably start with a multilvitamin (there is mixed evidence about this, but this is a pretty common recommendation). After that, fish oil (aim for 3000 mg/day total of EPA and DHA - ignore anything else in there, and DO NOT take flax oil, it's not useful for humans) and Vitamin D3 (2000 - 10000 IU/day) are pretty well researched, important for health and inflammation, and relatively inexpensive.
- Creatine is cheap and safe if it works for you. I personally don't respond to it. Try it out. Creatine should cause some immediate weight gain (not fat, just water in the muscles). I don't know how that might affect your lateral quickness. Post to comments if you have insight into this issue!
- ALWAYS shop around. I personally buy most everything from Netrition (no, I don't have any relationship to them other than customer). They usually ship quickly and have good prices and good customer service. Plus they send free t-shirts with your order, so now I have a drawer full of Netrition.com t-shirts that I wear to the gym all the time.
I personally take a multivitamin, quercetin (great for asthma and seasonal allergies), fish oil, 5000 IU D3, 100 mg K2, calcium carbonate in the morning, magnesium or ZMA at night, green tea extract (for the caffeine, mostly), 1 g C, 400 IU E, and am always throwing new stuff in there to try.
One last point - I tend to have a slightly laissez faire attitude towards supplements (I'm a little bit of a supplement junkie), but many openly sold, legal supplements do have potential side effectcs. Do some research before you just fill a basket with pills to take. Beware of anything that's supposed to affect hormone levels or stimulants. Not to say that they're all dangerous, just that I wouldn't pop them willy nilly without putting some thought into it.