Alrighty, after quite a bit more playing I've figured out some of the systems. It's not a complete guide, but I thought I'd share what I've learned for other new players.
The Diary records how many candid (masturbation) photos you've taken of your mom and sisters, and also keeps track of your current task hints. Read it by double-clicking its link.
The rest of the inventory items may be in different order than I list them here, depending on when or how you acquire them.
The Bug (aka generator Bugs at the supermarket) are used for showing the stats of the other actors, and tracking their location with the iphone10s. They cost 100 at the supermarket (aka cupermarket), although a dialog with Anka (in the prologue)/Anya/Anna and a note on the dev's blog imply they used to cost a LOT more. They can be stolen if you sneak into the back while Anya is on break (enter the back room between 12:00 and 13:00. The shoplifting event happened for me on the 4th time, which can be done as early as the second day if you hit the back room twice each day by entering in the first half of her lunch hour, then leaving (not hiding) with the Back link and entering again. Use it by clicking once on its link in your items, then on the actor (mom, sisters, stepdad) you want to bug.
The Mini-camera (aka nanny cam in the diary hint) is used for spying on locked rooms. Use it by clicking once on its link in your items, then on the link of the locked room (the bathroom while sisters shower, your sisters' bedroom most of the time, and your parents' bedroom at 21:00-22:00 while they're fucking). It costs 100 at the supermarket, but might have cost more at one point in development, since the diary implies you'd need to steal them. They CAN be stolen, which happened on the 7th time I snuck in the back during Anya's lunch break.
The iphone10s is needed to speak to the other actors, and collect and redeem excitement. It can be bought at the DK (aka the House of Culture) in the evening from the Huckster type, and costs 500. If you double-click it, it will list the accumulated excitement charge, and show the location of all bugged characters except your best friend Sasha. To redeem excitement, go to the DK, then use the iphone10s on the word "type". Your credits will update on your next move. If you're speaking to him, you'll need to back out to do this.
The Camera is obtained on the first Sunday when you celebrate your birthday. Don't miss it! Use it on your sisters and mom in certain rooms to initiate a photoshoot, which raises arousal by 1 for each shot. So far I've found shoots for Sveta in the kitchen, Mom in the kitchen, and Anya in the kitchen, her bedroom, her bedroom entrance while getting ready to go out in the morning (07:00-08:00 on weekdays, 10:00-11:00 on weekends), and your room while she's watching TV in the afternoon.
The cigarette is an aphrodisiac-doped cig you buy from the Huckster after you witness Anya's nighttime smoking, from 01:00-02:00 in the kitchen. After you watch her smoke once, the sill she smokes at will show up as an active link in the kitchen and you can buy the cigarette from the Huckster for 1500. Use the cigarette from your items on the sill, and next time Anya smokes, it will raise her arousal by 1 each minute until she's at around 65-70 arousal, at which point it will begin a masturbation scene. You can game the system during that hour to raise her arousal by double if you start a photoshoot in the kitchen, btw.
The Computer/nano-comp can be bought at the supermarket for 400, and shows up in your room instead of your items. You can use it to play World of Tanks, or watch DotA videos. Dev notes imply you'll be able to upgrade the bugs with your computer knowledge, but I might be wrong. If you use it ("nano-comp" link, not "Play in WoT") while your stepdad is in the room watching TV in the afternoon, he'll ask you to show it to him, then lays claim to it to play games every night from 23:00-Midnight. On the second night he plays, an event will trigger where he goes to the hospital and the "kill stepdad" plotline will begin. After that, he'll begin staying after midnight and watch porn until 02:00. Also, while writing this, I learned that if you hog the computer playing WoT in the evening until after 21:30, Anya will chase you off to do an essay, which will also raise her friendship with you. I'm not sure where this might lead but I plan to investigate further.
I'm going to stop here for now. Gonna go watch a movie with the fam.