Simple past or Present Perfect?

[dilodi83]

A. Hi Jane, I was looking for you. What have you been doing all day?
B. I have been making preparations for my journey to Japan.
A. What have you done? (Is "What did you do" possible if I consider that today's over already?)
B. I have cleaned my flat, I have taken my cat to Barbara's and I have also packed, but I
haven't collected the VISA yet (Can I use the simple past in these sentences if I consider the actions already over, or am I supposted to use only the present perfect since there's the expression "not yet" at the end of the sentence?)
A: Oh! You've been working very much! Did you have lunch?(Is it correct in this case the simple past? Or "Have you had lunch" might sound well?)
B. Not yet. I did not have time.
A. There's a good restaurant near here. We can have a beer and a sandwich together.
B. This is a great idea!

Now, on the basis of this dialogue, I have written in bold some questions in order to dispel some grammatical doubts I have...Could you please give me your opinions about that? I think there will be different opinions between American speakers and British ones...
Thanks so much for your help.

[5jj]

A. Hi Jane, I was looking for you.(Or: I have been looking for you.) What have you been doing all day?
B. I have been making preparations for my journey to Japan.
A. What have you done? (Is "What did you do" possible if I consider that today's over already?) As the previous question and answer have been present perfect constructions, 'What have you done?' is probably more natural. It is highly unlikely that you thought that today was not over when you asked the first question but decided that it was by the time you asked the second.
B. I have cleaned my flat, I have taken my cat to Barbara's and I have also packed, but I
haven't collected the VISA yet (Can I use the simple past in these sentences if I consider the actions already over, or am I supposted to use only the present perfect since there's the expression "not yet" at the end of the sentence?)It's not a question of 'supposed to' - it's a question of what comes naturally. Depending on how the speaker views the situatiions at the moment of speaking both past simple and present perfect are possible.
A: Oh! You've been working very much! Did you have lunch?(Is it correct in this case the simple past? Or "Have you had lunch" might sound well?)Both are possible. It depends a great deal on what tense B used in the previous uttterance.
B. Not yet. I did not have time. Same situation here.
A. There's a good restaurant near here. We can have a beer and a sandwich together.
B. This is a great idea!

Don't forget - grammar books describe only how most native speakers normally use the tenses/aspects. They do not say how these tenses/aspects must be used.