If you opened a pack and did not see what cards were in it for any reason, you can try the options below and get a text or visual view of the pack contents.
1. Peakmonsters:
Go to https://peakmonsters.com/@your_username/explorer and click the 'Open Packs' filter.
Peakmonsters does not always successfully show pack openings though, so you made to utilize one of the options below instead.
2. Find your Transaction ID on a Hive Block Explorer:
Go to https://hivehub.dev/@your_username or any other block explorer, if you prefer a different one (Replace your_username with yours). You should be able to find a transaction that reads "sm-open-pack" as pictured below, or "sm-open-all" if you opened more than 1 pack in the same transaction.
Click on the transaction and copy the full TX ID (a long string of letters and numbers). Then, open https://splintershare.info/, click the "Pack" icon (pictured below), and paste your transaction ID into the blank form next to the # symbol.
If for any reason you still can't see the contents of the pack, you can return to your Hive Block explorer, and that specific transaction. If you scroll down, you'll see UIDs for the cards in this pack. Highlight and copy that.
Finally, go to https://peakmonsters.com/@your_username/cards and paste the card ID in the search bar pictured below.
Unfortunately, you will need to copy each card ID one by one in this case, but it at least will show the TX went through, the pack was opened, and you successfully received the cards.