While again these laws may seem to be a collection of unrelated topics, they all have to do with the fact that the Israelites are people in a covenant relationship with God. Therefore their actions in each of these areas of life are supposed to reflect that relationship:
It was always a temptation to wait to fulfill the obligations they had to bring tithes of their income. Like us, the Israelites probably thought, "Next week/month I'll be able to give more, but right now, things are a bit tight." I understand that thinking, but it is not a good way to go. God expects obedience, and then blessing follows, not the other way around. Christians are not under the obligations of the law in these matters in the same way that the Israelites were obligated. In our own family, we decided upon a certain percentage of our income which we give to the LORD. It is still a struggle sometimes to stick to that commitment, but we have found that it is a good discipline, and the LORD has always provided for our needs. Someone wrote once that "You can't out-give God" and he is right.
The firstborn sons and animals were to be presented to the LORD. Of course, the humans were not to be sacrificed (!), but they were the LORD's as a reminder of how He had delivered the Israelites from Egypt, while the firstborn sons of the Egyptians had died in the tenth and final plague. Here are some Scriptures regarding this:
Exodus 13:2 "Consecrate to me every firstborn male. The first offspring of every womb among the Israelites belongs to me, whether man or animal."
Exodus 13:11-13 "After the LORD brings you into the land of the Canaanites and gives it to you, as he promised on oath to you and your forefathers, you are to give over to the LORD the first offspring of every womb. All the firstborn males of your livestock belong to the LORD. Redeem with a lamb every firstborn donkey, but if you do not redeem it, break its neck. Redeem every firstborn among your sons."
[Note that the above passage makes it clear that the Israelites were always to redeem their firstborn sons, never sacrifice them. They were to be redeemed, which meant that they were to be released by means of a payment. Also, in case you were wondering, as I was, why the donkeys were singled out in that passage to be either redeemed or have their necks broken, it is because they were considered an 'unclean' animal that was not supposed to be sacrificed to the LORD.]
Exodus 13:14-16 "In days to come, when your son asks you, 'What does this mean?' say to him, 'With a mighty hand the LORD brought us out of Egypt, out of the land of slavery. When Pharaoh stubbornly refused to let us go, the LORD killed every firstborn in Egypt, both man and animal. This is why I sacrifice to the LORD the first male offspring of every womb and redeem each of my firstborn sons.' And it will be like a sign on your hand and a symbol on your forehead that the LORD brought us out of Egypt with his mighty hand."
This passage spells out in greater detail the reason for the consecration of the firstborn to the LORD. It is interesting to me that the animals were also included, as they had been included in the plague on Egypt's firstborn. Perhaps it is because they were considered the wealth of their owner, sort of a portable bank account in a day without public banks. By including them, it is as if the LORD is saying that He had redeemed their lives and possessions from Egypt, and that He continued to be the source of their lives and wealth...indeed, of everything which they had.
A Priestly People
The Israelites were to avoid eating the meat of an animal torn by wild beasts. Instead, they were to give such meat to their dogs. The NIV Study Bible commentary noted that this was because such an animal would not have had the opportunity to have been drained of its blood, which the Israelites were forbidden to consume.
[Not to mention that this would be a great way to avoid diseases. God knows what He is doing, even when we don't.]
Interestingly, this verse was a law which was later specified for the members of the Aaronic priesthood.
God had already proclaimed to the Israelites that: "...Although the whole earth is mine, you will be for me a kingdom of priests and a holy nation..." (Exodus 19:5-6 NIV) In the same way that the priests were consecrated to the LORD for His service, every part of the Israelites' lives were to be consecrated to the LORD for His service. [And yes, that concept is as convicting to me as it is to you. No doubt each of us has areas of life which could be better given over to God for His use.]