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As a preliminary observation I wish you to make note that these Days are MEMORIALS,--every one of them!  Now God instituted some memorials just for the Israelites only, as Circumcision, for that  rite memorializes a Covenant between Him and the Israelites only.  BUT THE DAYS WE NOW CONSIDER MEMORIALIZE GOD'S GREAT CONTACTS WITH ALL MANKIND, AND THEREFORE ARE TO BE OBSERVED BY ALL RACES, THE WORLD OVER.  These Days memorialize some tremendous contact of God with all mankind and so are to be observed by all races, everywhere.
The Trumpets and Atonement Sabbaths memorialize GOD'S MESSAGES TO MANKIND--TO ALL RACES--as the Bible; The Divine or real message on Repentance, on Regeneration, so forth and so on, on the one hand, and OUR DIRE NEED OF REDEMPTION on the other (Atonement)....While the Feast of Tabernacles the Scriptures show plainly is an eight-day THANKSGIVING SEASON, the first and last days of which are Sabbaths regardless of on what days of the week they may fall.  Is gratitude merely a Jewish virtue?  Then this Thanksgiving Week is of worldwide significance.  We now pass to a more detailed study of these last three, which three constitute the autumnal cluster.

We now reach the last Memorable Day season:  THE FEAST OF TABERNACLES.  It is an eight-day affair. Lev. 23:39f; Num. 29:12-38.  Its days are catalogued and listed separately, one by one, for us in the Numbers passage.  The first day, verses 13f; "on the second day", v.17; "on the third day", v.20; "on the fourth day", v.23; "on the fifth day", v.26; "on the sixth day", v.29; "on the seventh day", v.32; and, "on the eight day", v.35.
In your own Bibles underscore each of these separate days.  On each of them we are to make "an offering made by fire", v.13.  This means (as you recall) an offering free from every carnal purpose.  It may be a money offering, or a reading of some special number of Bible chapters, or a making of spiritual Letters, or a giving of some special Testimony, or some other spiritual offering free from every crass purpose.
THE FIRST AND EIGHTH DAYS ARE SABBATHS, REGARDLESS OF ON WHAT DAYS OF THE WEEK THEY MAY FALL. Num. 29:12,35.  These are "Go-to-Service" days:  "Ye shall have a solemn assembly."
If we are alone in observance of any Special Sabbath and cannot therefore go up to a place of like believers on such day or days,--at set hour or hours in such day or days, retire for one's own personal Bible reading, prayers, and grateful and worshipful meditation. God bless His lone watchmen, wherever they may be, in every land!