How do I decline an offer at the combini?

When I'm at a grocery store or combini and the clerk offers me a plastic bag or to warm up my food, I get flustered and always say "douzo".

I think "iie" sounds wrong, but how else do I decline? What do I say if I don't wants a plastic bag cos I have my own canvas bag? Is it enough to say "daijoubu desu", or does that sound too vague?

You can say:
iidesu いいです, or
irimasen いりません

I'm Japanese and I always say "iie". There's nothing wrong with that, although it does help if you say it with a smile (which helps when saying anything). Or maybe the word you're looking for is "kekkou desu".

By the way, "douzo" is a word you use to offer something, so in this situation it's like saying "go ahead and do whatever you like" which is a little bit hard to clarify the intention. If you want the bag or warming, it's more common to say "onegaishimasu" or again a simple "hai".

For the plastic bag, "sono mama" works, means "as it is" - I think I learned this useful phrase on this site - works and I use it all the time now (at least twice today). Normally when I am buying a can of drink or something small.

Thats funny in my textbook they said hai is more formal, but everyone seems to be using it.

But i understand why people might think iie is not fitting, my textbook says you should never decline directly and say thinks like chotto...

But i assume that is only ment for personal relationships and not for shopping or other unpersonal encounters in daily life.

Thanks everybody! I think I'll go with "kekkou desu" and "sono mama" sounds like a good phrase.

And to Uco, yes, I ment to say "onegai shimasu", not "douzo", I do still mix up my phrases sometimes.

"nai" or "nai desu" can also be used when turning down a clerk's offer

yu,

Your phrase says "there is none/I don't have one," so might confuse the clerk...

You could use iranai 要らない No, thanks. I'll pass. (when offered something)(literal meaning: does not need.).

You could use iranai 要らない No, thanks. I'll pass. (when offered something)(literal meaning: does not need.).

Yeah.. except this would come off as pretty rude. Maybe ok to use to a friend or family member but when talking to someone else offering you something, 'iranai' isn't polite at all.