A buying list that leaves room for the celebration
Make the shopping list around the celebration you intend to have, rather than the displays you happen to see.

Name the occasions
A festival can involve several different purchases: something for the home, food for guests, gifts for relatives and perhaps clothes for a particular event. Putting all of these under one vague heading makes it easy to forget what has already been covered. Write the actual occasions and people first.
Then look at what is already available. Working lights, clean serving pieces and stored decorations may cover much of the list. This is not a demand to reuse everything forever; it is a way to see which new purchases would make a difference and which would merely repeat what is in a box.
Separate an item from its extras
A gift can involve wrapping, delivery and perhaps travel to collect it. A new decorative light set might need an appropriate mounting method. Include those related costs when deciding what fits your intended spending. A low item price can be misleading when the practical extras are left outside the calculation.
If several people are sharing the cost of a gift, agree on the total and the exact item before one person orders it. Keep the plan simple enough that everyone knows what they are contributing to. Avoid adding upgrades after agreement and assuming the others will be comfortable paying more.
Keep a short record of purchases as they happen. It can be a paper note rather than a new app. Mark the recipient or purpose next to each item so similar gifts are not bought twice. Also note deliveries that have not arrived; an order confirmation is not the same as having the gift ready.
Leave decisions that can wait
Some things are essential for your plans and others are optional. Make that distinction before browsing, while the imagined display is not yet influencing the list. If the necessary items use the available amount, the optional ones can stay unbought without the occasion becoming incomplete.
Consider timing as well as price. An item that arrives after the gathering is not useful for that event, even if the advertised reduction is large. Leave room for an ordinary alternative rather than relying on a tight delivery promise.
Afterwards, write down what was actually used. The unused stack of gift bags or extra serving bowls can inform next year's list. The goal is a celebration that suits the household, not a shopping record that looks impressive.