1st Tri? What you need and what might be nice to have IMHO.

I thought with spring coming up, it might be nice if people shared what they think you will need for your first tri and what you might not.

This is geared towards the sprint and possibly Olympic distances as I think there are definitely some things that change as you get up in distance. It's just my opinion.

Clothing
You need  things to swim, bike, and run in. You want to be comfortable in your clothes and you definitely don't want your clothes to be a distraction. You've got two options: you can try and wear the same thing for the whole race or you opt for some setup where you need to change one way or another (generally after the swim).

Wear the same thing: If you want to wear the same thing you need a tri top/and tri shorts or one piece tri shorts. Tri stuff is designed to be swam (swum?) in and to dry quickly. Tri shorts are different that bike shorts in that there is less padding and the chamois padding is designed to dry quicker. You can also run in tri shorts. If you opt for this, you'll wear the same thing from start to finish.

Change: You can wear a swim suit and then pull bike shorts over it and throw on a shirt as well in transition or you could just ride and run in your swim suit and throw on a shirt in transition. Most tris DO NOT have changing areas so don't plan on any nudity.

Tri clothing doesn't have to be horribly expensive and if you have an inkling you might stick with tris it's not a bad idea to pick up a tri top and tri shorts (or one piece)

Just one last thing....cotton is generally not recommended but it's not the end of the world IMHO especially for a sprint. You might get chafed a bit and it may be hard to put on when wet. If you've trained in cotton you can probably race in cotton. Just don't swim in it, it'll never dry.

Wetsuit
If your 1st tri is a pool swim you probably don't need a wetsuit. If it's an open water swim in warm water you can get away without a wetsuit. It all depends on the distance and water temps. Wetsuit will offer you some nice buoyancy but will slow you down in transition.

If you get tri clothing you wear that underneath the wetsuit so you can just peel off the wetsuit and get going.
You can't really wear shorts or board shorts under a wetsuit too cumbersome so you'd have to wear swim jammers or a speedo and then decide what you will put on in transition.

Minimum Gear List (you definitely NEED these)
Swim
     Googles

Bike
     A bike that is safe to ride with properly inflated tires. Anything will do from mountain bike to tri bike. Doesn't have to be expensive, just safe. Safe to ride means it handles safely and you know how to handle it safely. It shifts reasonably smoothly and has working brakes. Borrowed bikes are fine provided that race day isn't the FIRST day you ride it.
     A helmet that is not 10 years old. Helmets are required anyways but it's important that your helmet be a reasonable age and not have been exposed to any crashes. A crashed helmet is done don't ride with it again ($40 bike helmet)
     A water bottle and cage. Your bike should have a water bottle cage and you should have a water bottle ($8 cage and $12 water bottle)

Run
    You need a decent pair of running shoes. You'll probably also have biked in these so they serve 2 purposes. Just like a bike helmet, shoes are a relatively small investment in your knees during training. You can race on the same shoes you use during training. Can't recommend specific shoes but $60-120 should be a reasonable price range to buy running shoes. I would recommend running shoes not walking shoes, "sneakers" or even cross trainers

Transition
     Small hand towel to wipe off your feet (yes, that's it)
    
Nice to have
Nice pair of socks that are comfortable and wicking
Watch
Cyclometer to tell you how fast you are going
Garmin 305
Sunglasses
Hat for running
Race Belt (allows you to wear your race number with pins and easily turn it around from bike to run)
Chip strap (the race will give you one that is likely harsh, they make softer one's for around $5-10
Nicer bike (you can always have a nicer bike)
Clipless shoes and pedals (nice to get some more power out of your pedal stroke but will require you to change shoes from bike to run)

I am hoping some other folks will chime in and help out or offer their own lists. I also hope this helps some folks out for the spring.