Allegiant seats & bags

I have never flown Allegiant before but with the rising airline ticket prices, found a flight that was $100 less than any other carrier. But to get that price I had to decline reserving a seat ($ 30 RT) and checking a bag ($ 50 RT). Should I be aware of any problem with the OPEN seating (last ones on) and a very small carry on (backpack)? Will I be assured a seat? Will they make me check my backpack at the last minute and pay for it? Thanks.

1. Absolutely, subject to the involuntary denied boarding rules that come with every US airline ticket sold.

2. Depending on available space, you may be required to gate check your bag, but they're unlikely to charge you for it.

The problems that concern you will not be problems. However, their system is more than a little sneaky.
I assume you declined all the extras they automatically add on. However, you may not have noticed there are cheaper reserved seats. We do the $11.99 seats as our only add on.