Yes, the Items appear randomly. But why the hell would you train with just one kind of item?

I mean hell, thats just stupid. I can use basically any Item, and you can use different items differently with different characters.

Say DK. Using guns he can now fight at a distance, and try to lure an opponent to move in closer to you or do some damage without putting as much threat on yourself as you normally could.

However take a fast moving character like Shiek. She gets a ranged attack that doesn't take time to charge with a laser gun. She can now keep her distance and still pile on some damage safely.

Another thing for DK to use if he gets no gun is Bumpers and Bombs. Some well placed items like that can limit your opponents movements, thus making it easier for DK to land some of his harder hits.

Shiek, however, wouldn't want to do that with Bumbers and Bombs. She would be better suited for luring enemies into them, by either drawing or chasing them into them.