The particle shika

Hello, I'm trying to learn the mechanics of the particle しか through the help of my book, "a dictionary of Japanese particles". My understanding is that it is like saying 'only (blank) and nothing else'.

1) お母さん、今日のおやつこれしかないの？
Mom, is this all there is for snacks today? (this and nothing else?)

2) 期末テストまで、後たった一週間しかありません。
There is only a week left until final exams. (until final exams, there isn't any more than a week left.)
[quick question: what is tatta doing in this sentence?)

Also I have learned that after a verb, it's like saying 'there is no choice but'.

3) セミナーのレポートの締め切りは明後日。こうなったら徹夜するしかない 。
The deadline for the seminar report is tomorrow. Now I have no choice but to work on it all night.
[quick question: what is kou nattara doing here?)

4) 財布を盗まれたから、歩いて帰るしかない。
Because my wallet was stolen I have no choice but to walk home.

Besides the stumbling block 'quick questions' up there, I'm looking for insight from experts to be able to be comfortable with using ths particle. よろしく。

1)
In that sentence, これ can refer to a specific snack (e.g. cookie, cake, pie,,,) or the quantity of the snack. In the former case, there are only, for instance, cookies there, but the quantity might be enough. (Although （たった）これだけしかないの？ would be more commonly used for the latter case.)

2)
たった emphasizes the meaning of "only".

3)
明日: tomorrow
明後日: the day after tomorrow

こうなったら is a kind of conditional clause, but the meaning is more likely close to showing the cause/reason; "because the situation has come to this (= the deadline is the day after tomorrow)".

Toritoribe said:

1)
In that sentence, これ can refer to a specific snack (e.g. cookie, cake, pie,,,) or the quantity of the snack. In the former case, there are only, for instance, cookies there, but the quantity might be enough. (Although （たった）これだけしかないの？ would be more commonly used for the latter case.)

Click to expand...

Does the combination of dake and shika emphasize the meaning of only or what is the purpose of using both?

Generally, yes. だけ emphasizes "only". However, when used with the demonstratives (これ, それ, あれ), it usually shows the quantity, as I wrote in my post, probably because of the collocation that これだけ/それだけ/あれだけ performs as a set.