Went is the past tense of go. Use it when you are talking about something that happened before now eg I went to the supermarket this morning. I went to the supermarket yesterday. I went to the supermarket last week. etc
It depends. My local supermarket bags are quite strong enough to be re-used many times. Then there are 'bags-for-life' (often on sale in a supermarket) which should be very long lasting! Personally, I have my own shopping bags, so I don't need to use supermarket plastic carrier bags at all.