Hi,
Both things are pretty simple when you actually put some thought into it.
Firstly, ik this is a game, but if you were with a real girl, how would you proceed to have sex with her? FOREPLAY is the answer! (Make her cum)
Secondly - to give items such as gifts or accessories you need 2 things: high enough relationship level and her not being suspicious of you. If you end the night leaving her naked or/and covered in cum she becomes sus and won't accept anything besides normal gifts. It's best to skip few days or wait for loop reset. Shower scene has nothing to do with this. Also if 4-eyes comes in and sees her naked it's also a flag for her being sus of you.
Hope this helps,
Cheers