If the items are not listed on the items list, it means they are unique items that cannot be bought from or sold to NPCs. However, as more Floors are accessed, they may be featured in NPC shops.
You'll all linger in town until the morning of Day 5 (irl 26th of November) upon which you will visit the dungeon "The Hill's Sorrow" again. Timeskips from day to day will occur accordingly:
Day 2 -> Day 3 (irl 20th)
Day 3 -> Day 4 (irl 23th)
Day 4 -> Day 5 (irl 26th)
During that time, as usual mingle, visit NPCs, do small quests, whatever you wish to do. Just keep up with the timeskips accordingly. For in-day time skips (from noon to night for instance) Players may initiate them without GM's approval.
Regarding exp, remember to empty out your pool of exp as to not cause any confusion. So since it took you 100 exp to reach level 2, if you gained 110 exp since level 1, your current exp should be 10. Just to clarify any confusion, it takes 100 to reach level 2, 150 to reach level 3, 225 to reach level 4, etc. So if you are at level 2, with 10 exp and were to receive 800 exp, you would be at Level 5 with 97 exp.