That stinks that there is no recess! There are tons of things to do outside...weather permitting.
Students can collect materials from outside and classify, find the mass, volume, length, density, ect.
Students can take items outside and explore the melting process. You can even challenge students how to speed up or slow down the process. Which could lead to conductor/insulator conversation.
If there is recess equipment, students can do a force and motion scavengr hunt for force and motion then design their own recess equipment and describe what forces are being applied.
Earth and Space Science:
Students can search for examples of weather, erosion, and deposition out side and take photos of them to upload on some application such a seesaw and have a discussion as to what has caused the weather, erosion b or deposition.
Students can track the sunrise and sunset throughout the day through Shadows. Students can either use themselves, an item outside, or they could even build a statue themselves to incorporate art and then go outside throughout the day and either draw or take pictures of that item and the shadow. Students could analyze the data by charting how the shadow changes direction and size based on the suns position in the sky due to Earth's rotation.
Students can go outside and make predictions off the weather.
Students can go outside and collect various natural resources and then come back inside and complete a stem activity where these students have to build a house made of those natural resources and see the durability of it. Think of Three Little Pigs.
Students can go outside and create the solar system. You can even have student come up with the proper distances between each of the planets that way you could incorporate in math you could also have students build each of the planets to scale as well or come up with items to represent each planet to scale. Then go outside and form that.
Environment and Organisms
You could have the students be particular organism and then use 100 each of various items such as rice, beans, bowtie pasta, marshmallows or any other items and throw them on the ground or in the grass and then have the kids do a relay race to pick up as much of the food as they can. Then have students calculate how much of the food they got and come up with a percentage. This can lead into conversation about camouflage, adaptations, survival.
Students get you a simple scavenger hunt outside fighting different examples or even drawing and labeling different examples of the environment or places where organisms live. Maybe they see bugs living on a tree, or ant bed or bugs living under a rock. They can show how that organ is in the surviving and any of that organisms adaptations to survive in an environment.
You could have students split up into two uneven teams the smaller group half would be an organism such as a deer and the other part of the class with choose to be either shelter, water, food. The deer within have to match with someone from the other group so they would pair up with someone with water or someone with food or someone was shelter once they paired up then that person would become a deer and then you would repeat. If the deer cannot find shelter water or food then that deer dies and then they become water shelter or food. This is a really good simulation to show that the as a population of an organism increases the area's needs begin to decrease. And then as the organisms decreases then survival needs such as water food and shelter begin to increase.
You could do food web or food chain activities outside especially if you need a lot of room. Students can form a food web outside using pictures of an organism in yarn and they can see the inner connection between all of the different food chains and how one organism interacts with multiple food chains creating a food web.
You could also have each student be an animal and give them energy cards. For example, producers would have a green card, omnivores might have a brown card, herbivores would have a orange card, carnivores would have a red card,and a sun would have a yellow card. The sun would pass their eneegy card to producers, and as organisms "eat" other organisms the "eaten" organism passes on their energy cards. This is a great way to show flow of energy. You could even adjust the amount of animals to show that if one particular animal comes in and there's more of them, such as rabbits, than the grass would die more quickly because it's in unbalanced.
Those are just a few things that I can think of off the top of my head. I hope some of these help you explore science outside!