I voted "other"
How I answer largely depends on what lead-in the drive-through worker has given me.
If they ask "How can I help you today?" I usually start with "I'd like" or "I would like".
If they ask "Can I help you today?" The answer to their question is "Yes.." followed by what I would like.
If I'm not sure they carry something I'm looking for, or I have a special order I would like fulfulled, I ask "Can I get..." followed by the special request.
I never, ever, say "Let me have..." or "Give me...". I always say "please" and "thank you". I have chided my roommate before for not saying please and thank you or making eye contact with drive-through employees.
A typical order might go like this.
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Thank you for choosing Jack-in-the-Box. Can I take your order?
Yes, I would like a number five, with a diet coke, please.
Would you like the small, medium, or large sized coke and fries?
The small size, please, and can I get onion rings instead of fries?
You sure can. Your total is <whatever>. Please pull around to the window
Thank you very much
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Often times, I get a genuine "you're very welcome" in response. If I'm asked if I want ketchup, the response is "please" not "yeah". If I am unable to understand the drive through because of a bad speaker, I say "I beg your pardon?" or sometimes just "Pardon?" and if necessary, followed by "I'm sorry, but I cannot understand you". This is probably the most socially akward time for me at a drive through, because this can be taken as a criticism of the attendant, not the speaker, and such is not generally my intent.
Having worked that kind of job as a teen, I know that one customer's demeanor can make the difference between a good day on the job and a sucky one.
Some places around here, like Jack n the Box and Taco Bell, have pre-recorded greeters. In these instances, I used to say "no thank you" to the recording trying to sell me somthing, but then I realized that the social niceties didn't apply to the machine making person-talking noises, but rather, to the drive-through attendant. After much thought, I realize that in that situation, the first thing they hear you say is "No" without having said a word to you first, which has to be disenheartening in an already soul-draining job. So now, I ignore the recordings and just start by saying "I would like.."
This has gotten akward-feeling when the person taking my order happened to be the same as the person making the recording.