My DD started Reception last September. A few grains of advice, based on my experience:
School uniform - I completely overbought everything. In reality, she barely wore the dresses which were a bugger to iron and which were too summery to wear after the first half term. Buy the minimum you need to start with then stock up on more when you see what washes well/doesn't shrink in the tumble drier.
Groundhog Day - If you're doing pick-ups and drop-offs, don't underestimate the monotony - there and back 4 trips per day, 28 trips per week, 1120 trips over 40 weeks per school year, 7840 trips over 7 years in primary school. Then there's the 'hello's' to all the people you bump into on enroute and at the school gate - everyone's in a rush so there's no time to connect beyond that, just 'hello, hello, hello' ad infinitum.
Birthday Parties - Prepare yourself for an influx of 5th birthday invitations and how these parties will eat into your weekends. Buy your DD at least one superhero costume because a good 80% of said parties will be superhero-themed.
Before long, you'll be familiar with every Spiderman entertainer in your town and how good they are at doing backflips. Also, budget for all those 5th birthday party gifts. The kids' book section at TK Maxx is your friend.
Behaviour - My DD Matilda is known to our friends as 'Machillda" because of her chilled nature. Wow, did she defy this during her first term at school - hysterical tantrums due to the early starts and intensive days - kicking, biting, scratching, screaming... I lost count of the number of times I resorted to carrying her over my shoulder all the way to school as she kicked her shoes off in protest.
Matilda was born profoundly deaf and was entirely without access to sound until she got cochlear implants at almost 3 years old (cheers, lockdown). Therefore she started school with a significant speech & language delay - undoubtedly this contributed to her challenging behaviour as she had a vast amount of catching up to do which was overwhelming, daunting, and exhausting for her.
I'm relieved to say that after her first term, she settled in and has made astounding progress. In part due to her resilience, but also because we hit the jackpot with our catchment school - the teaching staff and SEN support are incredible, tailoring her education to meet her every need and checking in with me every step of the way. It's only after talking to friends about their experience of their DC starting school that I realise this isn't always the norm - therefore my advice is: don't hesitate to speak up if you sense something isn't right.