Is there any difference in meaning between 'I have' and 'I do have'?

"Do" is not necessary in this sentence, but it adds emphasis. This construction would usually be used when you are contradicting someone.

A: Can you tell me about this? Oh why am I asking you! You never have any information for me!

B: I do have some information you might be interested in.

or

A: Do you have any money for me?

B: No, but I do have some information you might be interested in.

You might also use it just for emphasis, like so:

Come see me before you leave. I do have some information you might be interested in, so don't forget to stop by.

In the US, the use of I have is widespread to indicate someone possesses something, but I do have adds an element of emphasis and, in that way, either contradicts what may have been an assumption that s/he did not have it or doubt about whether s/he had or has it. The doubt may have been general, like few people have (whatever), or specific, like chances are you've never had (whatever).

Yes

"I do have..." is more of a response to to a question with an alternative answer

"Do you have a pen ?" "(No, but) I do have a pencil"

"I do have.." could also imply an element of surprise

" Do you have 6 mm screw in your pocket?"

"I do have such a screw "

"do" is used for emphasis-by both British and American speakers.

"I don't have any homework tonight. I DO have some reading to do."

The difference is in tag questions and short answers.

Can you give me a ride home?

AM: Yes, I can.

BR: Yea, I can do.