59073
Can I say ～をごちそうさまです if I want to show gratitude for edible omiyage I’ve
received but have yet to finish? For example, I received a box of cookies
recently and want to say thank you as soon as possible, rather than after I’ve
finished the whole thing, in which case I’d say ～をごちそうさまでした. Does ～はおいしいです
accurately express this or is there a specific phrase for this situation?
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2018-05-30T02:54:20.390
59068
2018-05-30T11:05:13.993
2018-05-30T11:05:13.993
30008
16252
question
expressions food
Showing gratitude for omiyage yet to be completely finished (ごちそうさまです？）
ごちそうさまです is usually used for a meal, not for cookies or candies. ごちそうさまでした
(literally "it _was_ a good feast") clearly indicates you have finished it.
Saying おいしいです before eating sounds like "I know it's delicious."

In your case, you should simply say ありがとうございました. You may also add おいしそうです.
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2018-05-30T04:54:01.040
59071
2018-05-30T04:54:01.040
5010
59068
answer
If I understand your situation correctly, you received the omiyage, ate a
couple of them and will be meeting the person that gave them to you before
finishing them all. As naruto has answered ありがとうございました is the normal response.  
As far as adding おいしいです or something, whether you use past tense or present
depends on what you want to say.

あのお菓子はとてもおいしいですね！ could mean that you have had that kind before and think that
it is really good, or that it is the first time you had it and were surprised
at how good it was (level of surprise perhaps depending on emphasis when
said). You would need to add more information to differentiate between these
two meanings. In this case, whether you had one or finished all of them is
irrelevant.

While using the past tense （とても）おいしかったです。would refer specifically to the ones
they gave you, and not that brand or kind of snack as a whole. This sounds
more like you finished them all, but that does not necessarily have to be
true.

Note that I'm just using 「あのお菓子は」 because I don't know what it actually is.
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2018-05-30T05:40:30.707
59073
2018-05-30T05:40:30.707
1761
59068
answer