Ideas for an anniversary on a budget

My [30m] girlfriend [30f] and I are celebrating our 4-year anniversary in a few weeks and, to put it bluntly, we're broke.

We're in the middle of saving ahead of our mortgage application & house move, so our spending is at an all-time low. It's not an exaggeration to say we're spending pretty much nothing on things that aren't essential (food, bills etc). As things are pared to the bone, paying to go out to a (fancy) restaurant is off the table, as is paying to do any activity that isn't free/incredibly cheap. Even getting a cheap takeaway can't be guaranteed right now

We both know this anniversary won’t be a fancy occasion, but I’ve been trying to come up with ideas for what I can do to still make the day special. My girlfriend has really been busting her ass on getting things sorted for our house and I want to make sure she has a great day off from it all.

We both have the day off work, so I know the day is free. Here’s what I’ve come up with so far…

• For gifts, I bought one gift several months ago before we started saving hard, so I have to give. I'll be able to get a nice card without breaking the bank and I'll look into getting some flowers too. I'm also thinking a full-body massage at home in front of the TV/in bed
• We have free cinema memberships (through work), so I can look to see if they're showing any films she likes (but the showings aren't up for the date yet)
• Weather permitting, we can go on a walk around some of the parks near our house and take a picnic
• Our first date was playing board games, so I can look to recreate it (but we own a lot of games now and have been playing a lot anyway, so this would need a fancy twist)
• In terms of food, we’ve got a bit of a stockpile at home (which is helping us live cheaply), so I'll look into any nice home cooked meals I can do with what we have. We did chocolate-covered strawberries for Valentines this year, so I could do a basic "chocolate fondue" with some more fruit, biscuits etc

Does anyone have any other suggestions for things to do that aren't just "sex"?

Tl;dr Our 4-year anniversary is coming up and we’re broke. What can we do to have a good time?