In book 1 of Melachim (Kings) Chapter 8 it says that there were only 2 tablets in the Ark. What happened to the Mon (manna) and Moses' staff? Weren't they supposed to be in there as well?
The meforshim explain that it was put "in front of" the ark, not inside the ark. Thus, it was in a separate container. As shown in Yirmiyahu 2:31, it was brought out then to show them. Rav Hirsch says in Beshalach 16:34
As Hashem had commanded Moshe long before, at the first sending of the Manna, later on when the ark of the tablets of the covenant was in existence, Aharon laid the flask of Manna in front of it.
Rashi on 16:33 says
and deposit it before the Lord: Before the Ark. This verse was not said until the Tent of Meeting was built, but it was written here in the section dealing with the manna. —
The Gemara says that either the two sets of tablets (whole and broken) or only the whole tablets were in the Ark
The contents of the Ark has been debated through the centuries. The general consensus is that the first tablets containing the Ten Commandments, which were broken by Moses, and the second tablets, which remained intact, were contained in the Ark (Bava Batra 14b). According to one opinion in the Talmud, both Tablets were together in the Ark; according to another, there were two Arks, and each contained one set of Tablets (Berakhot 8b).
Note that the text in the Talmud Bavli says that both luchos were in the same ark. However, the citation is brought to show that the manna was not in the ark and that is the quote as written.
The Yerushalmi in Shekalim says explicitly that there were two arks, one for each set of luchos but there are rabbanan who say there was only one Ark containing both
דף כד,ב פרק ו הלכה א גמרא התורה נתונה בתוכו ואחד שהיו שברי לוחות נתונין בתוכו זה שהיתה התורה נתונה בתוכו היה מונח באהל מועד הדא הוא דכתיב (במדבר יד) וארון ברית ה' ומשה לא משו מקרב המחנה זה שהיו שברי לוחות נתונין בתוכו היה נכנס ויוצא עמהן ופעמים שהיה מתראה עמהן ורבנן אמרי ארון א' היה ופעם אחת יצא בימי עלי ונשבה
Daf 24b, Perek 6 Halacha 1 The torah was placed in it and one held the broken Luchos in it. The one that had the Torah (whole luchos) in it stayed in the Ohel Moed as it says (Bamidbar 14) "and the aron of the bris and Moshe did not move from the midst of the camp" The one that held the broken luchos would come in and go out with them and at times was seen among them There are rabbis who say that there was only one aron and one time it was removed in the time of Eli and captured [by the P'lishtim].