Avrohom Cried for Sarah
בראשית כג,ב: וַתָּמָּת שָּרָּה בְּקִרְּיַת אַרְּבַע הִוא חֶבְּרוֹן בְּאֶרֶץ כְּנָּעַן וַיָּבֹא אַבְּרָּהָּם לִסְּפֹד לְּשָּרָּה וְּלִבְּכֹתָּהּ:
The Baal HaTurim writes that the letter Kaf is small to indicate that Avrohom's crying for the death of Sarah was limited. The Gemara (Moed Katan 27b) explains that the first three days after a death are for crying and the last four days of the "shivoh" are for eulogy. Avrohom was at Har HaMoriah when he became aware of Sarah's death and immediately set out for Chevron. This was a three-day trip, as we find that from Chevron to Har HaMoriah for Akeidas Yitzchak took three days (22:4). When he reached home the main time for crying had passed, so his crying was limited. It seems that this would also explain why he first eulogized her, and only afterwards cried for her passing, "lispode l'Soroh v'livkosoh."
The letter Kaf (20) underscores the difference between the age of Sarah when she dies (127) and the age of Yaacov at his death (147). They were linked in many ways including being the first and last ones buried in the Cave of the Machpaleh.
Poison
בראשית כד,לג: וַיֻּישָׂם לְּפָּנָּיו לֶאֱכֹל וַיֹאמֶר לֹא אֹכַל עַד אִם־דִּבַרְּתִּי דְּבָּרָּי וַיֹאמֶר דַּבֵּר:
Playing on the word "va'Yusam", which, when spelt with a 'Samech' has connotations of poison. The Baal haTurim explains that they placed poison in his food (so that he should die, and they would then take all the money that he brought with him per Da'as Zekeinim) and then quickly sat down to eat so that he should not notice.
The only other time the word "va'Yusam" appears in the Torah is at the end of Sefer Bereshis (in connection with Yosef), where the Torah writes "va'Yusam bo'Oron be'Mitzrayim", a hint that they wanted to kill Eliezer and place his body in a coffin.
But he did notice, and when he said "I will not eat until ... ", adding "I am the servant of Avrohom", he meant that, as a servant of Avrohom, he was not used to eating before reciting the Berachos of 'al netilas yadayim' and 'hamotzi Lechem min haaretz'. He hoped that the Kos shel Berachah would work in his favor, and his faith was well-founded; an angel came and switched his plate with that of Besuel, who ate the poison and died.
Yitzchak Brought Rivkah to the Tent
בראשית כד, סז: וַיְבִאֶהָ יִצְּחָּק הָּאֹהֱלָּה שָּרָּה אִמּוֹ וַיִּקַּח אֶת־רִבְּקָּה וַתְּהִי־לוֹ לְּאִשָּה וַיֶּאֱהָּבֶהָ וַיִּנָּחֵם יִצְּחָּק אַחֲרֵי אִמּוֹ:
The Torah uses the same word in "וַיְבִאֶהָ" ("vayevi'ehoh"), when it writes "And he brought her (Chavah) to Adam" (2:22), in Melachim 1 (3:1), "And he (Shlomo) brought her (the daughter of Paroh) to the city of David, and in Daniel (9:14), "HaShem hastened it (the calamity) and brought it upon us".
The Baal haTurim explains how all this hints at the Chazal, which describes how, when Shlomo married the daughter of Paroh, an angel came and stuck a cane in the sea from which grew the Kingdom of Rome. Hence the Pasuk states, "And he brought her to the city of Dovid ... and HaShem hastened it and brought it upon us". Before marrying the daughter of Paroh, Shlomo ruled over the Heaven; after marrying her, he ruled over the earth. This is similar to Adam, who was expelled from his Celestial connections following his sin; whereas by Yitzchak it was the opposite - because with the advent of Rivkah, the Shechinah rested on his tent, just like it had done when Sarah was there, as the Medrash explains, creating Heavenly connections that he had not previously had.