Both are non-essential items. Your AR will fire without them and they can be installed later when PSA delivers. You won't get a BHO on an empty mag but as long as you are aware of it, no big deal. If your grip screw bottoms out before it tightens (it shouldn't but it might), you may have to find a local substitute. Any old 1/4" tooth washer will work of the external or internal tooth flavor. I've seen both kinds in LPK's. A standard flat or lock washer will do the trick, too.
I don't know of a substitute or hack for a missing bolt catch plunger.
I've ordered many LPK's from PSA and have never had even one part missing. I don't why it is hit and miss with them. I guess it depends who is working QC that day.
Suggestion: It will cost you about $50 to $70 to get one home- but in my opinion, anybody that tinkers with AR's should have a spare LPK in the cabinet for situations such as this.
It will cover you if have parts missing from another kit, if you loose a part during assembly, or if something breaks in your lower during operation.
If you don't want to buy a complete LPK you can always get one of these: (no FCG)
http://www.midwayusa.com/product/862947/ar-stoner-customizable-lower-receiver-parts-kit-ar-15Or cheaper yet- this "oops" kit-
http://www.midwayusa.com/product/949287/cmmg-ar-15-lower-pin-and-spring-kitIf you don't want to fire your rifle without the bolt catch and are unsure when PSA will deliver, you can order one of these kits. Midway usually ships same or next day on in stock items and their shipping is only $5 for standard mail. $5 more for the UPS upgrade and you'll probably have your stuff by Wed. of next week depending on what state you live in. Midway is in Missouri. If you want to make your shipping worth it, just buy something else. I just picked up this single point sling from them and I am totally impressed with it.
http://www.midwayusa.com/product/213539/midwayusa-tactical-single-point-sling'just looking for a quick fix for you.